average body weight for height
Beginner's Guide to Backpacking
Backpacking gear selection and hiking tips.
- Sleeping Bag Temperature Ratings - II
People differ greatly in their metabolism. Cora, for example, sleeps comfortably beside me in a bag with nearly double the amount of insulation mine has. She uses a bag rated to 0 degrees for summer backpacking even though the temperature almost never dips below freezing, and she's rarely too warm. It should be noted that Cora gets cold faster than a skinny dipper in January. At the opposite extreme, I've slept in a tent at 17,000 feet on McKinley in a sleeping bag rated to -15 when the temperature outside the tent was -40. I got some sleep, but I can't say I was terribly comfortable, and I was wearing every scrap of clothing I'd brought, including four pile hats and hoods. Each person also varies in their need for insulation from time to time. If you go to bed wet, cold, exhausted, poorly fed and dehydrated, you'll need a lot warmer bag to be comfortable than if you go to bed warm, dry and full to the brim with a final cup of hot chocolate.
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.
- Vapor Barrier and Radiant Barrier Liners
Vapor Barrier and Radiant Barrier Liners
Winter backpackers can add a lot of warmth to their sleeping bags by using a vapor-barrier liner: a six-foot-long bag made of a waterproof, non-breathable coated material. A VB liner stops the heat loss caused by evaporation of insensible perspiration, the water you constantly lose through your skin just because your skin is not watertight like a plastic bag. A VB liner also stops the evaporation of sensible perspiration, the kind you produce when you're overheating, so you need to regulate your temperature carefully by shedding clothing if you start to sweat. Used properly, a VB liner can allow you to sleep comfortably in temperatures 10 or 15 degrees lower than you could without a liner. Used improperly, a VB liner will awaken you with the feeling you've encamped in tropical Borneo.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.
- Sleeping Bag Size, Shape and Fit
Size, Shape and Fit
Your sleeping bag's shape and fit greatly influence its warmth. Form-fitting bags contoured to fit a human body are called mummies because, like your mother when you were a kid, they hug you close and keep you warm (actually, they were named for the preserved bodies of dead Egyptians, which they resemble in shape, but I'd rather fall asleep thinking about my definition than the real one.) More expansive bags, for those of substantial girth or those who like more wiggle room, are known variously as wide mummies or barrels (I can see my mother frowning); even more capacious bags are known as semi-rectangular bags. Fully rectangular bags (named, of course, for really square moms) are for slumber parties and warm-weather car-camping. They're too bulky and heavy for backpacking.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 be