Nearly all manufacturers supply a temperature rating with their bags. These ratings are based on the manufacturer's estimate of what the average person will need on an average night when the moon is full and Pisces is rising in the east. There's usually nothing too scientific in how they arrive at their guess, and even if there is, your own experience may differ. However, most people can make an educated guess, based on comparison with companions at home and during car-camping trips, whether they sleep warmer or cooler than average. People who always feel like a Popsicle should buy a bag rated to 5 or 10 degrees colder than the average low temperature they expect. People who find themselves frolicking up the trail in shorts when everyone else is swaddled in goose down can probably get away with a bag rated down to 5 or 10 degrees warmer than the average low.

VB liners provide a crucial additional benefit: They help keep your sleeping bag dry. In severe cold, without a VB liner, the moisture that escapes from your body will condense inside your insulation, whether it's down or a synthetic, reducing its effectiveness. During my second expedition to Alaska, in 1980, the down bags used by my two companions collapsed completely as moisture built up during our 13-day epic ascent of the south face of Mt. Hunter. Peter Metcalf said later that his bag became so useless he would simply have thrown it away if it hadn't cost so much. During Will Steger's dog-sled expedition to the North Pole, the team's synthetic sleeping bags accumulated 35 pounds of ice through condensation because the team wasn't using VB liners. In 1982, when both Peter and I used VB liners inside our bags during our ascent of Reality Ridge on McKinley, both of our bags stayed dry and lofty, in large part because of the liners, but also because we took every possible opportunity to dry our bags.

While preparing for an Alaskan expedition in 1983, I took the vapor-barrier concept into the realm of fanaticism and decided I needed to back up the coated nylon VB liner I normally used with a giant plastic bag. Unfortunately, the requisite size of bag was only available in 100-bag rolls. Fortunately, I was able to persuade a friend to go in with me on the purchase of a roll. Even more fortunately, my friend remained my friend after this rather shameless imposition in an obsessive cause. A normal coated nylon vapor barrier is all you really need, even in severe cold. Summer backpackers need not concern themselves with vapor barriers at all.

For a time in the early 1980s, manufacturers experimented with a different kind of liner, one designed to block the loss of heat in the form of infrared radiation. Texolite was the most common brand name. The material did indeed prove its worth in the synthetic sleeping bags of the day, where adding the weight of the liner provided more additional warmth than adding an equivalent weight of insulation. The same was not true of good down bags, however, where a user needing additional warmth was better off adding more down than adding Texolite.

Texolite's problem, at least in the minds of summer users, was that the material was also a pretty effective vapor barrier. People complained that Texolite bags had too limited a comfort range: They found themselves overheating too easily. Partisans of vapor barriers like equipment designer Jack Stephenson would argue that all these complainers wanted was the license to sweat and soak their insulation, and that the better solution would have been for overheated users to take off some clothing. Despite such cogent arguments, however, the consumer rules in our society, and Texolite and its competitors have gone the way of the dodo bird, at least for now.

Snug-fitting bags are generally warmer than loose-fitting ones, in part because there is less cold air and icy sleeping bag surrounding you when you first climb in, so the bags warm up faster. More importantly, a snug-fitting bag, combined with an effective hood, helps prevent your movements from pumping warm air out of the mouth of the bag, then drawing cold air in. A bag that’s too snug, however, will give you claustrophobia, so be sure to slip inside the bag at the shop before buying. Most good shops will let you try on a bag if you take off your shoes and look civilized. Many winter campers like to buy an extra-long bag to provide room at the foot for items that should be kept from freezing, such as water bottles and boots.

Several more details are worth considering. A hood is an integral part of all good mummy bags. It's designed so that tightening a drawstring cinches down the bag's mouth until only your face is exposed. In addition to a hood, good winter bags often have an insulation-filled collar that closes down over your shoulders and around your neck to further reduce the escape of warm air. Most bags are supplied with full-length zippers to make it easier to get in and out of them. That zipper can be another avenue of heat loss unless it's protected by a draft tube, a long, insulation-filled tube on the inside of the bag that covers the zipper. Cold feet seem to be a perennial problem on chilly nights. Better bags often have extra insulation in the foot area. Don't worry unduly about the other details of construction, such as which particular baffle system is used in a down bag, or whether a synthetic bag is described as having shingle or double-overlapping quilt construction. All of the methods used by reputable manufacturers work just fine.

Most sleeping bags have an outer shell of porous nylon that makes no claim to be waterproof. Even as a novice, I knew that sleeping unprotected in the rain would guarantee a soaking wet bag. But what about in winter? Shouldn't it be possible to sleep in the open, since it would be so cold that snow wouldn't melt on the bag? Such a tactic, if successful, would save the weight of a tent during winter climbs.

In 1977, Joe Kaelin and I set out to test that theory on our first effort to climb a major route in Rocky Mountain National Park in the wintertime. Already impressed with the cold, we bivouacked at the base of the face under a boulder, then started up the climb at first light. Darkness caught us only halfway up the route, and we searched futilely for some kind of sheltered bivouac site. At last we gave up, scooped out two body-sized ledges in the midst of an unprotected gully and crawled into our bags.

At midnight I awoke feeling that my sleeping bag had grown tremendously heavy. Spindrift pouring down the narrow slot above us had completely buried our bags. I pushed away the snow as I best I could from inside the bag and tried to go back to sleep, but in vain. Two hours later, with sleep impossible and our bags rapidly becoming drenched, we began soloing up the face by headlamp. We summited a few hours after sunrise.

As we had so convincingly demonstrated, enough heat escapes through your sleeping bag to melt snow or frost lying on the shell fabric. You don't need to do anything as foolish as exposing your bag to a non-stop spindrift cascade to get your bag damp in the winter. Frost sifts down from tent walls, while spindrift blows in each time the door is opened. Meltwater drips from snowcave roofs while wind carries snow into the entrance. Even in summer, condensation dripping from tent walls can gradually dampen your bag. A sleeping bag with a waterproof-breathable or water-resistant shell will help keep your bag dry. Such bags are also a bit warmer because of the windproofness of the shell, but I wouldn't buy such a bag just for that reason.

If you and your mate are like otters, who like to sleep half on top of each other, you may be interested in buying sleeping bags that can zip together into one giant love-nest. One bag must have a right-hand zipper, the other a left. In addition, the zippers must be the same size. Most sleeping bag manufacturers offer bags that will zip together. Another option for highly compatible couples is to buy a semi-rectangular bag that can be unzipped completely so it lies flat like a comforter. The unfolded bag is then zipped to a simple cotton or nylon sheet with a zipper along its perimeter. The result is, again, a giant love-nest, but this time one that has insulation only on top. The sheets that make this transformation possible are known variously as doublers, couplers or couplets. The advantage of a doubler is that it lets you carry sleeping gear for two that weighs just a pound more than sleeping gear for one. Cora and I find that doublers work well down to about 40 degrees or so. Below that, we sleep cold because it's impossible to cinch down the mouth of the bag to prevent the escape of warm air.

As a kid, you may have slept in your backyard on a slab of open-cell foam or a three-inch thick air-mattress that made you dizzy as a top from the effort of inflating it. If either of these two items are still lingering in your closet, let them linger. Open-cell foam – the kind that crushes under body weight to about one-quarter of its original thickness – is generally too heavy, water-absorbing and bulky for backpacking. Normal air mattresses, while comfortable in warm weather, are chilly when the ground is cold because air circulates freely inside them, drawing heat from your body through convection.

For years, all I ever used as a sleeping pad while backpacking in the summer was a sheet of half-inch-thick closed-cell foam. Closed-cell foam is lightweight and cheap, doesn't absorb water and is highly durable. It's also rather uncomfortable to sleep on if you, like me, have spent years being spoiled rotten on an acre-wide Sealy Pamperpedic that hogs three-quarters of the bedroom floor. In the backcountry I always secretly envied my friends the luxury afforded by their Therm-A-Rests – essentially, air-mattresses filled with open-cell foam – even as I derided them as heavy, leak-prone, even a touch bourgeois. My friends just smiled, indulging me in my tirades. Finally my inflated ego collapsed under the complaints of my bruised hips, and Cora and I bought a pair of Therm-A-Rests.

What luxury! Sure, they weigh 2 pounds 5 ounces each rather than 10 ounces like my old closed-cell foam pad, but the comfort is worth it (or maybe I'm just so much more tired after lugging the extra weight up the trail that I could sleep on porcupine hide). The open-cell foam prevents convection, so the pads are warm, while the waterproof, air-tight shell keeps the foam dry. After our first tantalizing taste of backwoods luxury, Cora and I plunged further into decadence and bought Therm-A-Rest Chairs, 10-ounce fabric and webbing devices that convert a Therm-A-Rest into a legless chair that sits directly on the ground. No more aching backs while cooking dinner or lazing about watching the sunset! Therm-A-Rest is no longer the only brand of foam-filled air mattress available, but they do have a proven track record. A leaky or inferior brand could prove to be a let-down.

Therm-A-Rests do have one drawback. Although they’re quite warm enough for three-season use, they don’t provide enough insulation for winter, in my opinion. For winter camping, I use two half-inch thick closed-cell foam pads stacked on top of each other.

I find a pillow even more essential for comfortable sleep in the woods than I do at home. Rather than carry an actual pillow, I stuff an extra sweater into my sleeping-bag stuff sack, the stout nylon bag that comes with every decent sleeping bag.

You can also prolong your bag's life by keeping it clean. That means always sleeping in a tent or on a ground sheet, not directly on dirt, and wearing clothing when you go to bed. It's a lot easier to wash long underwear than it is to wash a sleeping bag. Spot-clean stained areas as soon as possible after they get dirty rather than washing the entire bag. Airing your bag in the sun for a few hours after each trip will help kill any musty odors that develop.

When your entire bag finally does need washing, usually after several seasons of hard use, take it to a commercial laundromat with a large-capacity, front-loading washing machine. Do not use a top-loading, agitator-type machine, which can easily ruin your bag through rough handling. Front-loading machines tumble your bag and put much less stress on batts of synthetic insulation and the fragile baffles that hold your down in place. Use a soap that dissolves well in the local water. Your goal is not only to get soap into the bag to get it clean, but to get all the soap back out. Soap residues in any bag can cause clumping of the insulation and loss of loft. Special down soaps dissolve easily and rinse out well, but aren't really necessary and may not be strong enough to remove stains from the shell. Dry-cleaning is not advisable. Some experts argue that dry-cleaning strips oil from down and makes it brittle. Others argue that few dry-cleaners take the care to make sure that all the dissolved dirt is rinsed out of the bag with clean solvent. In any case, the fumes from solvent residues can give you headaches or worse.

If you must wash your bag at home, fill a bathtub with warm water and a little soap. Immerse the bag gently, knead the soapy water into the bag, then drain and rinse repeatedly until no more soap bubbles percolate through the shell. Press – don't wring – the water from the bag and gently lift it from the tub. Wet down is heavy, and the weight of it can rip the baffles loose from their moorings if the bag is manhandled. Dry the bag in a tumble dryer on low heat, which can take several hours. Be sure the bag is thoroughly dry before storing it. With a down bag, you may need to fluff the bag vigorously to break up clumps of down and restore the full loft. Think of this as an exercise in feathering your own nest.

"My candle burns at both ends;
It will not last the night;
But, ah, my foes, and oh, my friends,
It gives a lovely light."
Edna St. Vincent Millay, A Few Figs from Thistles, 1920

Three friends – Lisa Cotter, Jenny Ball and Cindy Carey – were planning an expedition to Mt. McKinley, a peak which is infamous for the arctic gales that beset its slopes. Accordingly, they wanted to get some experience camping in high winds. They decided, a bit naively, that the ideal location for a training trip was the Boulderfield on Longs Peak in Rocky Mountain National Park. The Boulderfield is a bleak, rocky plain, far above timberline, that is raked by hurricane-force winds in the wintertime. One stormy February weekend a few months before the expedition, they invited me to join them and we headed up. Winter days go fast, and the last pink glow of sunset was abandoning the peaks to the north when we finally got the tents erect in the stiff wind and crawled inside. Jenny and I, together in one tent, cooked dinner by the light of our headlamps. I noticed that the battery powering my headlamp was growing weak. No worries, I thought; we're only here one night, I'll only need my headlamp for another few minutes and besides, I have a spare battery.

Soon after the last sip of hot chocolate, we doused the headlamps and plunged the tent into darkness. The wind began to grow stronger. The tent strained against the gusts as the taut fabric crackled noisily. I had been dozing restlessly for no more than half an hour when a loud snap! like a breaking tree limb jarred me awake. The wind had broken one of the tent poles. An instant later the second one, now unsupported, fractured as well and the tent began flapping and billowing like a giant jellyfish gone mad. I lunged for my headlamp and flicked it on to survey the damage. The beam faintly illuminated a gaping rip in the fabric. Afraid the tent would be destroyed completely and all of our extra gear would blow away, Jenny and I began packing frantically. Suddenly my headlamp winked out, its battery shot. Fumbling in the dark, I plugged in my spare battery, confident that our lack of light was merely a temporary annoyance. Then I discovered that it, too, had somehow become drained. A minute later, Jenny's headlamp failed as well. Fortunately, she also had a spare battery. Unfortunately, it too was dead. Embarrassed now as well as desperate, we borrowed a headlamp from Cindy and Lisa, finished stowing our gear and packed up the tattered remnants of the tent. Cindy and Lisa's tent had also suffered a broken pole; a second pole was badly bent, but the tent, although lopsided, was still standing. The four of us squeezed inside and waited for dawn. When morning finally arrived, we abandoned our plans to climb Longs Peak and scurried for home.

If we hadn't been able to borrow a headlamp from Lisa and Cindy, Jenny and I would have been in much worse trouble. The odds would have been good that some valuable piece of equipment would have blown away in the dark as we struggled to pack all our gear. It just goes to show that when darkness reigns, a headlamp is de-light.

If you're a typical summer backpacker, you'll never need to worry about your tent exploding around your ears, but you're quite likely to need a reliable headlamp or flashlight, if only to investigate those mysterious midnight gnawing sounds that prove to be a porcupine chewing into your pack.

A headlamp is just a bulb and a reflector mounted on an elastic headband. With some models, the battery case is also attached to the headband; with others, it rides in a pocket, where the battery stays warmer and therefore lasts longer. The disadvantage of that system, of course, is that you then have a wire running from a pocket to your head, which not only makes you look like an android, but also gives malicious branches the perfect handle to rip your headlamp from your head. Headlamps let you use both hands to pitch your tent, cook, or pack, which is why Cora and I prefer them over flashlights. For trail walking, however, you'll often find that carrying the headlamp in your hands makes it easier to pick out obstacles in the trail. The reason? Moving the light away from your eyes gives better definition to the scene by casting longer and more pronounced shadows.

When traveling solo, I carry a full-size Petzl headlamp, plus a four-ounce Mini-Maglite headlamp (so I can change batteries and bulbs in the main headlamp in the dark), plus spare batteries and a spare bulb for the miniature headlamp. I do a lot of nighttime hiking on my way to sunrise photo ops, so I put a halogen bulb and a hefty 4.5 volt battery into the Petzl. The combination will throw a usable beam of light for 100 yards – great for off-trail bushwhacking in the dark.

The best batteries for the environment and for your pocketbook over the long run are rechargeable nicads. They cost more initially, and you have to buy a battery charger as well, but they have a useful life of 500 to 1000 charges, which makes them far more economical over time. One disadvantage is that nicads hold less energy than comparable alkaline batteries. A second disadvantage is that even fully charged, never-used nicads will gradually go dead over a period of two or three months and have to be recharged. Throwaway alkaline batteries are convenient because of their long shelf life, but they contain nasty acids and heavy metals that pollute groundwater if these toxins seep out through the bottom of a landfill. In cold weather, nicads have the advantage over alkalines because their power output doesn't drop off as fast as alkalines' power does. The best batteries for really severe cold, however, are the non-rechargeable lithiums. Nothing else will power a headlamp reliably at temperatures below zero.

To light your stove, you'll need either a cigarette lighter or matches. Cora and I carry both because lighters, although convenient, have a disconcerting habit of failing if the lighter gets wet or the operator's hands are damp. Matches provide an excellent backup if they're carefully secured inside a plastic bag without holes. For even greater security, you can find waterproof, strike-anywhere matches in backpacking stores. It's a good idea to throw an extra cigarette lighter into the repair kit or some other secure place, just in case.

People whose boots are heavy or uncomfortable sometimes bring a pair of lightweight slippers or sandals to change into once they reach camp. People whose feet are chronically cold in their sleeping bags at night may enjoy a pair of down booties. On snowy trips, it's convenient to have some means of walking around in the snow without having to put your stiff, heavy ski boots or mountaineering boots back on. One solution on really cold trips is to bring insulated nylon overboots. During the day, you wear the overboots over your regular boots. Overboots cover up the lugged boot sole, so you'll also need to use skis, crampons or snowshoes to provide traction as you travel. At night, you can slip on the overboots alone when you just need to step outside the tent to perform some chore. Another solution at night is to put a heavy-duty stuff sack over either your inner boots (if you normally wear double boots) or over your socks. If you use a big stuff sack, such as the one containing your sleeping bag, the stuff sack will reach to your knees. You can keep the stuff sack from falling down around your ankles by tightening the cord lock on the stuff sack's drawstring. On Alaskan expeditions, I sometimes brought two extra stuff sacks for just this purpose. Just be sure you stay off any hard-packed snow slopes while wearing your stuff sacks. I still remember stepping out of my tent at 17,200 feet on McKinley's West Buttress and immediately slipping, falling and sliding 20 feet down the wind-packed snow. I stood up, unhurt, took one step back toward the tent and immediately fell down again. Returning to the tent was impossible until I hit on the idea of just removing the stuff sacks. My textured wool socks gripped the polished snow securely and I walked back to the tent with ease.

Summer backpackers in wooded regions rarely need sunglasses. However, if you're hiking above timberline across early summer's lingering snowfields, sunglasses can prevent a lot of uncomfortable squinting or worse. Snowblindness – essentially, sunburn of the cornea of the eye – can cause severe pain for several days. Don't count on pain to warn you of the danger, however; the pain begins several hours after the damage is done. If you find yourself squinting heavily, you should put on your sunglasses. Time is the only cure for snowblindness, although victims normally get some relief by remaining in a darkened room or otherwise shielding their eyes from light. Desert hikers frequently find sunglasses a pleasure, and winter backpackers in snow country should routinely carry both sunglasses and goggles. In an emergency, almost any way of reducing the amount of light hitting your eyes will help. I once cut a slit in my wilderness permit to make an impromptu pair of sunglasses. On another occasion, after my first and only bout of snowblindness, I taped up my goggles so that only a slit remained. The system relieved some of the pain, but made skiing interesting, since I could only see one narrow strip of snow at a time. People who have eyesight so poor they would have trouble hiking out if their glasses were broken should bring a spare pair.

A large plastic garbage bag slipped over your pack with the mouth pointing down will keep your pack dry during a nighttime shower. You can use a bit of duct tape from your repair kit to patch minor rips and extend the bag's useful life.

After Cora had $4,000 worth of dental work done several years ago, we became remarkably conscientious about bringing toothbrushes, toothpaste and floss on all our backpacking trips, even short ones. Our personal hygiene kit also contains (at Cora's insistence) a package of pre-moistened towelettes and a hair brush. Even I insist on bringing toilet paper, unlike some hard-cores I know. A trowel is valuable for burying wastes (more on this subject later).

Embarrassed as I may be to admit my addiction to a quintessentially citified piece of gear, I find a watch to be an important item of wilderness equipment. Primarily I use it to keep track of our pace and timing. Will we make the campsite by dark? Will we make the top of the pass in time to shoot the sunrise? A watch also lets you time the cooking of your pasta and rice.

A simple repair kit can save you a lot of grief even on a short trip. A basic kit might include:

spare parts for the stove
a little duct tape or ripstop repair tape to patch a hole in a tent, rain jacket, insulated parka or sleeping bag
extra clevis pins and split rings (if you're carrying an external frame pack which uses those devices to attach the pack bag to the frame)
bit of extra string to use as spare shoelaces and for lashing this to that
A more elaborate repair kit for a trip lasting a week or longer might also contain:
wire for lashing together broken whatevers
needle-nose pliers with wire-cutters to force the aforementioned wire into place
heavy-duty sewing awl (Speedy Stitcher is my favorite brand), stout thread and scrap of heavy fabric
five-inch length of copper pipe with an inside diameter just larger than the diameter of your tent poles, to patch a broken pole
spare two-inch quick-release buckle to replace the buckle on your pack’s hip belt.

If you've been clutching your wallet ever more tightly as you read chapter after chapter on what to buy, it's time to relax. With the exception of first-aid kits and water-purification devices, we're done with discussing what you need to own. Now, with the buying spree behind us, we can move on to everyone's favorite topic: what's for dinner.

"I live not in myself, but I become
Portion of that around me: and to me
High mountains are a feeling, but the hum
Of human cities torture."
Lord Byron, Childe Harold's Pilgrimage, 1812

The road to hell is paved with good packs used badly. I still wince at the thought of my own mistakes. There was the time I finished a five-day ascent of Yosemite's 3,000-vertical-foot El Capitan, then packed 60 pounds of steel and aluminum rock-climbing hardware into a day pack designed for 25-pound loads and hauled it seven miles back down to my campsite. And the time seven friends and I climbed Alaska's 16,237-foot Mt. Sanford. At the beginning of the expedition, we made two trips, carrying half our gear each time, from the bush landing strip to the foot of the glacier. Coming out, however, we were too eager for showers, pizza and rock 'n roll to adopt such a sane approach, so we decided to make only one trip, carrying everything in one gigantic load. At the foot of the glacier, I filled my gargantuan internal-frame pack to the brim, loosened the pack lid's extension straps to their limit, crammed in some more, then lashed a fiberglass sled and heavy mountaineering skis on top. My pack must have weighed 90 pounds—about two-thirds as much as I did. I felt like an Olympic weight-lifter doing the clean-and-jerk on a gold-medal weight each time I hoisted my pack. After two repetitions, it became impossible to lift it without assistance, and I was forced to ask for help in getting it on after each rest stop for the remainder of the trailless nine-mile hike out over the tundra. Fortunately, someone else agreed to carry the 12-gauge shotgun we'd brought as grizzly insurance. A couple of years later, I carried a similar-size load of camera gear into the Grand Canyon to photograph a rafting expedition. I had packed the pack while it was sitting on the tail gate of my pickup so I could slip it on without actually lifting it off the ground. That meant, however, that all the way into the canyon I could never set the pack down without finding a tailgate-high, flat-topped rock to set it on. People stopped me on the trail repeatedly and said things like, "That's the biggest pack I've ever seen." At first I was secretly proud. Then the pain got too great and I would just smile through tight lips and keep walking.

At first, you may want to carry the book pack you once used to haul books to school without breaking your arm. You'll quickly find, however, that you've entered a race between your growing dissatisfaction with the book pack's capacity and comfort and its accelerating tendency to explode at its flimsy zippers. I'm rooting for the zipper explosion, because that will give you the perfect excuse to buy a day pack that will last you for a decade and make your hiking days a pleasure.

The day packs I like share several features. First, they pamper your shoulders with amply padded shoulder straps. Second, they protect your spine from steely-hearted, back-stabbing pieces of equipment with a foam-padded panel that covers the entire back of the pack. (Let's clarify a bit of nomenclature here: the back of your pack faces your back, while the front faces away, so you can think of yourself as a two-headed push-me pull-you as you walk down the trail.) Larger-capacity day packs, which are designed for higher loads, may protect your back with both foam padding and a sheet of stiff plastic. The plastic sheet also helps transfer weight to your hips. A well-padded hip belt makes that weight transfer more comfortable, but beware: few day packs let you adjust the height at which the pack rides relative to your waist. The wrong size day pack can leave you with a hip belt that puts the squeeze on your stomach—and that extra cheese danish you gluttonously gobbled—not your hips.

I prefer day packs with simple drawstring closures at the top, referred to as top-loading packs. The alternative is a panel-loading pack with a long, U-shaped zipper arcing across the front panel. Panel-loading packs provide convenient access to all your gear, but have one serious Achilles' heel. Even the most stout zipper tends to break or wear out eventually, particularly if it's used in sandy regions. Sand and grit get into the zipper teeth, then wear out the slider from the inside. You'll start zipping your pack shut one day and find that the zipper is unzipping itself behind the slider just as fast as you zip it together in front. With many panel-loading day packs, a zipper failure leaves you with no good way to close your pack and retain the contents inside. A top-loading pack with a drawstring can't fail in this manner. Panel-loaders also have the disadvantage that they must be laid flat on their backs to access the contents – an unappealing prospect when the ground is a sea of mud, since any mud that clings to the back of the pack is immediately transferred to your clothing when you put the pack on.

Your day pack should have a few other features. Look for a large pocket in the pack lid, but be aware that it's one of Murphy's laws that you'll never have enough room in that pocket for all the essential items that you want to be immediately accessible. Many designers include a flat pocket for maps underneath the lid, but I prefer instead to put the map in a zippered pouch hanging from my shoulder straps, where it's more accessible, and use the “map pocket” solely for invaluable items like car keys and my wallet. Once those items are safely stowed, I refrain from unzipping that pocket until I’m back at the car, to ensure my keys won’t slip out unnoticed and disappear between two unmovable boulders.

Better day packs have compression straps along the sides of the pack. These straps, usually two or three to a side, allow you to compress the load and prevent the contents from swaying to and fro, which can upset your balance when you're boulder-hopping, log-balancing, skiing or swinging through the jungle with Tarzan in hot pursuit. Compression straps also give you a convenient way to lash on extra clothing and equipment, like a fly rod, tripod or skis. I like to slide my skis tail-first down through the compression straps, then lash the tips together with a short accessory strap. Lashing the tips helps keep the skis from pivoting back and forth and whacking you in the head when you walk. Be sure the tails don't drop down so low they hook the back of your knees or catch on the ground when you're walking down a steep hill. To further simplify attaching skis, look for a day pack with a quick-release buckle on the top compression strap instead of a ladder buckle, which must be painstakingly rethreaded if you undo it completely.

Most day packs provide lash patches on either the front of the pack or the lid. Lash patches are small leather or synthetic swatches of material sewn to the pack with slots behind them to accommodate lash straps, short lengths of nylon webbing with buckles on the end, used for attaching gear that won't fit inside. Technical day packs (meaning packs designed for climbers) include an ice-ax loop, a small loop of webbing at the bottom of the pack that makes attaching an ice ax convenient. Ice axes are not just for demented people who like to climb frozen waterfalls; many early-season peak-baggers carry them to stop a slip while crossing hard-frozen snowfields in the early morning. If your ambitions include such ascents, look for a day pack with an ice-ax loop. Be aware, however, that an ice ax is useless unless you know how to use it. Novice mountaineers should seek competent instruction from a qualified mountaineering school or highly experienced friends.

My first multi-day pack was an external-frame Kelty with an olive-drab pack bag, purchased in the early 1970s when I was a young teen. It possessed all the virtues that external frames still have today and served me well on my first backpacking trips into the Sierras with my father. The frame itself was built of stout aluminum tubing in the form of an abbreviated ladder about three feet high. The two vertical members on the sides were curved to fit the curve of my spine. Four horizontal cross members provided rigidity and strength. The pack bag had one top-loading main compartment closed with a simple fabric flap and several zippered side pockets. Broad mesh bands across the back of the pack forced the pack bag to ride slightly away from my back, permitting a cooling breeze to dry my sweat. The rigid frame effectively transferred most of the weight to the padded hip belt, where it belonged – your hips can carry more weight, much longer, than your shoulders. The shoulder straps served primarily to prevent the pack from toppling over backwards. The forward curve of the frame as it rose above my shoulders allowed me to lash heavy items high, with the weight centered almost directly over my hips, so I could walk with a comfortable, nearly upright stance.

The same rigid frame that made carrying my Kelty so comfortable on smooth trails, however, proved to be a liability when my father and I left the trail and scrambled up a long, talus-choked couloir to the summit of Mt. Agassiz, a 13,891-foot peak that provided a stunning view of the surreal turquoise blue lakes at the base of the Palisades. With the rigid frame strapped on tightly with the hip belt and shoulder straps, I felt like I was wearing a body cast that prevented the natural bending and twisting required to keep my balance on the uneven, boulder-strewn slope. Carrying the weight high compounded the problem because it raised my center of gravity and made me top-heavy. The efficient way to travel on talus is to move rhythmically from rock to rock in a flowing, dynamic balance. That goal was thwarted, however, by the pack's rigidity and high center of gravity. Similar experiences in the late 1960s led Greg Lowe to create the first parallel-stave internal-frame packs. His pioneering design is now the basis of most of the internal-frame packs manufactured today.

Lowe's goal was the first winter ascent of the north face of the Grand Teton. For that, he needed a large-capacity pack with a suspension comfortable enough to handle significant weight that would also allow him to climb effectively. His solution was a pack with two internal aluminum staves set vertically and parallel to each other in the back of the pack bag. With no horizontal cross-members to stiffen the frame, the pack could flex enough to permit a long reach for a good hold or a graceful jump turn while skiing steep snow. The staves were bent to fit the natural curve of the back, so the weight rode very close to the body, reducing the top-heavy feeling of carrying an external frame and preventing the pack bag from swaying to and fro and throwing the climber or skier off-balance. Other pack makers jumped on the bandwagon and soon internal-frame packs were the standard for mountaineers, backcountry skiers and an increasing number of backpackers as well. I bought my first internal-frame pack in 1978, shortly before my first expedition to Alaska, and I've been using them almost exclusively ever since.

Not all internal-frame packs have two parallel aluminum stays like Lowe’s original design. Some slant the two stays inward like a V or even crossed like an X. Others use a single stay, reinforced with a polyethylene frame sheet, sometimes reinforced still further with flexible plastic or carbon-fiber stays running vertically along the edges of the frame sheet. No one design has emerged as demonstrably superior; instead, comfort seems to depend on the care with which each basic design is implemented.

Internal-frames do have disadvantages. The back of your shirt is guaranteed to be soaked with sweat after an hour or two of walking because no cooling breeze can force itself into the paper-thin gap between your pack and your back. The load typically rides lower than in an external frame, which is good for balance but more tiring because it enforces a vaguely simian forward-leaning posture. Internal frames are also less forgiving of packing errors such as stowing the heaviest items at the bottom, and it’s harder to lash on a big, awkwardly shaped load, like a hefty tripod, that won’t fit inside the pack bag. (I'll discuss pack packing in more detail later.) Internal-frames are usually more expensive as well.

If you plan to stick mostly to summer trails and want to save money, consider an external-frame pack. If winter snowshoe or ski trips or lots of off-trail scrambling are in your plans, then an internal frame is a better bet. External-frames are usually targeted at budget-oriented consumers, which means manufacturers generally haven’t put as much design effort into the comfort of the harness as the best internal-frame manufacturers. For that reason, I prefer a top-quality internal-frame when I’m carrying a massive load.

Travel packs, all of which have internal frames, allow you to hide the suspension behind a fabric panel or to remove the suspension completely. At one end of the spectrum, travel packs can be glorified suitcases with uncomfortably skimpy shoulder straps. You wouldn't want to carry one on your back farther than the VIP slots of a small parking lot. At the spectrum's other end are full-featured packs suitable for week-long treks. Despite pack makers' best efforts, however, even sophisticated travel packs tend to be a compromise between carrying comfort on the trail and durability while traveling. My preference is to protect my expedition-grade pack with a big duffel bag when I travel by air.

Be sure to take these additional precautions before heading to the airport. First, make sure your pack/duffel bag combo doesn't exceed the weight limit for a single piece of luggage. Excess baggage charges add up very fast. Seventy pounds is the limit on most domestic flights. Limits on small planes and overseas flights may be less, depending on the carrier. Some duffel bags and packs have double-pull zippers, with two adjacent sliders that let you unzip the bag from either end. Consider locking those two zipper pulls together to discourage casual theft. Don't bring any backpacking fuel on board, whether in your stove, in your fuel bottle or in the form of butane cartridges, whether attached to your stove or not. Carrying fuel on board is illegal because it creates an extreme fire hazard. After emptying your stove and fuel bottle, triple bag them to prevent fumes from contaminating clothing or food. One plastic bag won't necessarily stop all odors from penetrating your goodies. Bill Baker and I learned this the hard way during a nine-day, 150-mile sea-kayak journey in Kenai Fjords National Park. Bill had just purchased two brand-new fiberglass kayaks. Two days out, we discovered that the pilot crackers we'd brought as a mainstay were absorbing fiberglass odors right through the heavy plastic bags in which we'd stored them. Not only did the crackers taste bad, they gave us rude, fiberglass-tainted burps that lasted for hours.

Your first concern, when buying a new backpack, is making sure it fits. Finding such a pack, however, is not quite as simple as it might seem.

In 1983, I guided an expedition on Mt. McKinley. My assistant, Janet Gelman, was a former college ski racer who had once broken her back in a skiing accident. One week into the three-week expedition, her old injury began to hurt again. She was carrying a nearly-new, top-quality internal-frame pack almost identical to the one I was carrying in relative comfort. (I say relative because carrying 60 pounds for eight hours will make your shoulders sore no matter what pack you're carrying.) Like most women, she had a much shorter torso than the average male. Like most “unisex” packs, hers had been designed for the average male torso. The result was a pack that always rode too low on her hips and put too much strain on her back, no matter how she adjusted it. Finally, in desperation, she took a stout sewing awl called a Speedy Stitcher and modified the suspension of her pack so it would ride higher on her back – a painstaking operation that took several numb-fingered hours at 14,300 feet.

The moral of this story may seem obvious: make sure your pack fits before you buy it. As my assistant found out, however, and as I've experienced myself with other packs, it can take a week or two of use, combined with constant fiddling, to get a pack's suspension tweaked to perfection. When buying a pack, look for a suspension that is as adjustable as possible. If you can, select a pack that seems to fit best when using the middle portion of the adjustment range, giving you the option of altering the fit in either direction. Women who find that men's packs don't fit should seek out a pack from one of the companies that now make packs specifically for women. Even these provide no guarantee of a perfect fit, however. The hip belt on Cora's first internal-frame pack, although designed specifically for women, had insufficient travel to cinch snugly about her small hips. We had to shorten the belt with a Speedy Stitcher to make it comfortable for her. The very best packs are made in several sizes each for both men and women. A knowledgeable salesman can be invaluable in selecting the right size pack – another reason to visit a specialty shop.

Trying on an empty pack tells you nothing about the fit, so most good outdoor shops keep sand bags of varying weights in the pack department. Toss 25 or 30 pounds into the pack you're considering, then walk around the shop for a few minutes. You'll quickly gain a much better feel for the pack's load-carrying comfort.

Internal- and external-frame packs share similarities in the way they're fitted, even if the mechanism for making alterations is quite different. The first and most important adjustment is the distance between the hip belt and the point where the upper end of the shoulder straps attaches to the frame or pack bag. Let's call this the pack's torso-length adjustment. If this distance is too short, the pack's hip belt will ride too high, encircling your stomach instead of your hips when the shoulder straps are adjusted properly. If this distance is too long, the hip belt will ride too low even if you tighten the shoulder straps as far as they will go. A low-rider hip belt, chic though it may be, will constrict the muscles in your buttocks and the outside of your hips, causing discomfort and fatigue, and potentially causing back pain. This is the problem my assistant guide experienced on McKinley. If the torso-length adjustment is set correctly, the hip belt will cradle the tops of your hip bones and most of the pack's weight will ride comfortably on your hips. Normally, you'll only need to adjust the torso length once during the life of the pack. With the torso length correct, all the other adjustments should fall into place easily.

Sophisticated external-frame packs allow you to adjust the torso length by moving the attachment points of both the shoulder straps and the hip belt. On less expensive frame packs, the upper end of the shoulder straps attaches directly to a fixed horizontal frame member, so the height of the shoulder-strap attachment cannot be adjusted. Some of these inexpensive frame packs allow you to adjust the height of the hip belt's attachment to the frame; others provide different frame sizes to fit different torso lengths. The least expensive frame packs come in one size. Avoid these unless you're positive they fit perfectly and your primary concern is saving money.

To determine if the torso length you've selected for an external-frame pack is correct, first load the pack and slip it on. Adjust the shoulder straps to approximately the right fit, neither so tight that they squeeze your shoulders uncomfortably, nor so loose the pack seems to be dragging you over backwards. Then fasten the hip belt and cinch it down firmly. It should snugly cup the high points of your pelvis. The pack's weight should feel like it's riding mostly on your hips. Now, if need be, tighten the shoulder straps slightly. The shoulder straps should be horizontal where they attach to the pack frame. In other words, the attachment point should be the same height as the top of your shoulders. If necessary, adjust the torso length until both hip belt and shoulder straps fit correctly. Once you've got the torso length correct, check a few other points. Are the shoulder straps acting like vampires, drawing blood from your neck because they're too close together? Are they acting like teens at a junior high mixer, so far apart that they weight the outermost parts of your shoulders uncomfortably? Good packs let you adjust the distance between the shoulder straps to fit your anatomy.

Internal-frame packs use a different method to adjust the torso length. With most internal frames, the upper end of the shoulder straps attaches to the shoulder yoke, which is positioned approximately between your shoulder blades. The height of this shoulder yoke can be adjusted up or down, usually via some arrangement of straps and buckles. Regardless of the method, the goal is the same as with an external-frame pack: proper positioning of the shoulder straps in relation to the hip belt so that the pack's weight rides primarily on your hips, with the shoulder straps serving mostly to prevent the pack from swaying dramatically from side to side or falling over backwards.

The advantage of attaching the shoulder straps to a shoulder yoke is that the straps wrap more comfortably around your shoulders than they do with an external frame. The disadvantage of the shoulder-yoke design is the greater potential for the pack to sway. To prevent swaying, and to further reduce the pressure on your shoulders, internal-frame packs have shoulder-stabilizer straps, also known as load-lifter straps. These straps attach to the shoulder straps at about your clavicle, then extend upward at a 45-degree angle to the pack's aluminum staves. Snug down your shoulder-stabilizer straps, then loosen the shoulder straps a bit and the result is almost magical relief for your aching shoulders as the load shifts even more completely to your hip belt. When your hips start to complain, tighten the shoulder straps again, loosen the shoulder-stabilizers a little, and shift some weight back to your shoulders. These adjustments can be made on the trail, almost without breaking stride. Only the best external-frame packs offer shoulder-stabilizer straps.

Good internal frames can be fine-tuned even further. In an effort to allow your hips to move independently of your shoulders, the hip belt on most internal frames fastens to a lumbar pad that rides in the small of your back. By moving the attachment points of the hip belt relatively close to each other rather than positioning them at the outside corners of the pack bag, your hips can rock up and down like a teeter-totter when you walk without pushing the pack bag up and down at the same time. That reduces fatigue and increases comfort, but introduces the possibility that your pack could roll side to side like a barrel on your back. To reduce that motion, pack designers introduced hip stabilizer straps that run from the bottom corners of the pack bag to the hip belt. They should be loosened each time you remove your pack, then tightened again after you've put on your pack and snugged down your hip belt. Keep them lightly tensioned for greater comfort while trail-walking; snug them down further for greater stability while skiing and off-trail scrambling.

Hip stabilizer straps serve a second function on some top-quality internal frames: transferring weight more evenly to the hip belt. By running the straps diagonally upward from the bottom corners of the pack bag to the front of the hip belt, the pack’s weight is distributed evenly and comfortably around the entire circumference of your pelvis. This design reduces pressure on the sensitive front corners of your pelvis and alleviates the tendency of the pack to sag uncomfortably onto your butt. Why don’t all internal frame packs have this seemingly simple feature? Because making it work right requires a frame that offers a structural anchoring point in the bottom corners of the pack bag, not just floppy fabric. Engineering this properly requires additional labor and materials, which drives up the cost. For killer loads, however, I regard this feature as indispensable.

The final adjustment, almost universal now on internal frames and increasingly common on external frames, involves the sternum strap, which connects the shoulder straps at the level of your sternum. This strap lets you fine tune where the shoulder straps ride on your shoulders – close together for narrow-shouldered people, farther apart for broader-shouldered people. The point where the sternum strap attaches to the shoulder straps can usually be adjusted up and down so the sternum strap rides at a comfortable height across your chest.
By now you may feel that buying a modern pack means you'll spend half your vacation reading instructions and yanking on puzzling pieces of webbing rather than enjoying the wilderness. Perhaps pack makers are actually engaged in a diabolical plot to keep befuddled novices near the trail head so they won't overcrowd the pack makers' favorite wilderness valleys. With a little perseverance, however, you can master your pack's intricacies, defeat this sinister scheme, and stride forth confidently into the wilds. Whatever you may read in the instructions, no matter whether you're carrying an external frame or an internal frame, your comfort is the final arbiter. Keep tweaking that suspension until it feels right, even if it means stopping in the middle of the hike to fiddle with it. Preventive maintenance on your pack's suspension will repay you many times over.

Like day packs, the pack bags that accompany both external- and internal-frame packs come in two basic styles: top-loading, in which you stuff everything in the top while holding the pack upright, and panel-loading, in which you lay the pack flat on its back and unzip a large panel on the pack's front. Simple top-loading internal frames close with a single drawstring. More complex internal frames have, in addition, a spindrift collar, essentially an extension of the main pack body that closes over the contents when the pack is full to keep blowing snow from sneaking into the pack. The pack lid on an internal frame with a spindrift collar often "floats." Adjustable straps allow the lid to be raised to cover an overstuffed pack, or be lowered to cover the pack's opening when the load is smaller. Floating lids and spindrift collars are particularly useful to winter campers, long-distance trekkers and people who backpack with kids, all of whom need room for large volumes of clothing and food.

Most external-frame packs, whether top-loading or panel-loading, have a light aluminum framework called the hold-open bar at the top of the pack bag. On a top-loading pack, the hold-open bar keeps the mouth of the bag open for easy loading. On a panel-loader, it provides structure to the pack bag when the front panel is zipped open, again making loading easier. Large-capacity external frames often have a frame extension that rises above the hold-open bar. The extension provides additional lashing points when your gear begins multiplying like a family of love-starved guppies.

In general, I prefer top-loading packs, whether internal frame or external frame, because they have no zippers to blow out and because you don't have to lay the suspension side flat in the mud to get at the contents. The disadvantage of a top-loader, particularly one with a single, undivided compartment, is that you have to think carefully about what goes in first, because everything else will go in on top, burying the items on the bottom and making them inconvenient to get at when you're on the trail. The solution, of course, is to put items you won't need during the day, like your tent, sleeping bag and stove, at the bottom. The problem of accessibility is manageable, but some people still prefer panel-loaders because they provide easy access to all of their gear at any time.

Pack bags for both internal and external frames are normally made of pack cloth, a tough nylon weighing about 8 ounces per square yard that is easily durable enough for normal use, or 500 denier Cordura nylon, which is slightly stronger. (Denier refers to the weight of a certain length of yarn. Higher denier means greater strength.) Packs made of 1000 denier Cordura are overkill unless you’re planning to drag your pack up Mt. Everest.

If you choose an internal-frame, you'll need a pack with a capacity of 3,000 to 4,500 cubic inches for trips of two to three days. A capacity of 4,500 to 6,000 cubic inches should work well for a week-long trek. Anything over 6,000 is for a full-blown Alaskan or Himalayan expedition. The capacity of an external frame's pack bag can be 1,500 or 2,000 cubic inches smaller because it's assumed you'll be lashing your sleeping bag and tent to the frame above and below the pack bag. A good way to add convenience and a little extra capacity to an internal-frame pack is buy the accessory side pockets that many manufacturers offer. These usually attach to the compression straps on the side of the pack. Side pockets do make you a bit more broad of beam, which is a disadvantage when canyoneering and bushwhacking.