Chapter 17

Sleeping Bags, Sleeping Pads, and Vapor Barriers

You can endure great hardship as long as you can sleep warm. Sir Francis Galton, The Art of Travel, 1867

Introduction  Types  Fitting  Ratings  Materials  Insulations  Cost  Care  Glossary  Comparisons  Sleeping Pads  Repairs  Vapor Barriers

SLEEPING BAGS ARE great for keeping warm in airports and stations, on overnight trains and buses, and for crashing on a new friend's floor. They're also useful for insulating yourself from El Cheapo Hotel bedding. A good sleeping bag adds more flexibility for the traveler than any other item in the pack.

Of course not all backpackers need a sleeping bag. If you expect to be in a hotel, hostel, or warm train every night you probably don't. If you're hostel-hopping out of a daypack (about 2000 cubic inches or 33 liters) you may not have room. Nevertheless, most backpackers have some kind of sleeping bag.

Since my travel is characterized by a certain amount of outdoor accommodation, I almost always want a light but warm sleeping bag. I use a 20º F (-7º C) down mummy with a standard nylon cover. Its weight is less than 2.5 pounds (1.1 kgs.), volume is an easy-stuffing 7x14 inches (18x36 cm.), and current cost is only $110. Following is everything I know about sleeping bags learned in the course of buying the wrong bag before my second travel adventure, and this suitable one after my third.

There is no perfect sleeping bag for all seasons, conditions, or uses, however. Every bag involves trade-offs between weight, stuff-size, comfort, warmth, weather resistance, durability, and cost. Fortunately the technology has advanced to an admirable state, and with fierce competition (dozens of American brands alone) quality and value are mostly the rule.

The Mummy and the Semi-Rectangular

For travel the two sleeping bag designs to consider are the two which are the most weight and stuff-size efficient: the mummy style and the semi-rectangular style.

The mummy is the most efficient in retaining body heat since it incorporates a hood which, when fully battened-down, leaves only a small circle of your face exposed to the cold. On warmer nights the hood need not be used.

The roomier semi-rectangular lacks a hood but has a drawstring closure which can be cinched over your shoulders. (A mummy will do this also.) Some semi-rectangular bags have zippers extending across the foot section allowing the bag to open into a comforter, which is a very useful feature. A semi-rectangular will weigh at least five ounces (140 g.) more than a mummy for a given temperature rating, and substantial headgear will also be required to stay warm at that rating.

Choosing the Right Size

The roominess of a bag depends upon your and its dimensions across the chest, hips, and feet. A spacious bag will not be as warm as a slightly tighter one since the bigger bag has more inside air for the body to heat. If it's too tight, however, colds spots are formed where the insulation is compressed. You will also be less comfortable putting on additional layers of clothing should the conditions become extreme for the bag's temperature rating.

Hence a five footer carrying a a six-footer's bag shoulders excess weight, volume, and expense, and sleeps colder in return, although tucking extra length under the feet helps considerably.

Sleeping bag models usually come in two or three sizes. The only way to properly size a bag is to get in four or five different ones. Outdoor shops allow and expect this. For me, roominess across the shoulders is a paramount consideration since I don't like feeling too constricted.

Temperature Ratings

Manufacturers give their bags temperature ratings to reflect the low temperature someone can expect to maintain homeostasis, which is a more or less constant, comfortable body temperature. These numbers are somewhat accurate given three conditions.

First, the testing for these ratings is done in rooms where the air remains still. And we all know what an effect wind has on relative temperature (wind chill). In other words, if you're sleeping in the open in a twenty-degree nylon-shelled bag on a twenty degree night with a five mile per hour wind, you will absolutely freeze your butt off since nylon isn't windproof.

Second, when testing the manufacturers use abundant insulation underneath the bag--equivalent to a full-length Standard Thermarest, which is 1.5 inches (3.8 cm.) thick and provides more insulation than most travelers carry. Thus if you use a 3/8 inch (1 cm.) foam pad you will definitely feel cold at extreme conditions. (Sleeping pads are discussed at the end of this chapter.)

The final factor is individual metabolism. In the same bag some sleep comfortably while others feel cold. This variation ranges up to 15º F (8º C). Since I sleep on the cold side I would choose a slightly warmer bag for a given condition, which for safety and comfort's sake is a good idea regardless of metabolism.

Note that if you're hungry or dehydrated your ability to withstand cold (or, more correctly, manufacture heat) will be adversely affected. A hot drink and warm stew work wonders on a cold night.

Sleeping Bag Materials

Inner shells are usually made of fine nylon or polyester, although some bags have a cotton/polyester inner liner. Cotton/polyester has less of a sticky or clammy feel against bare skin at warmer temperatures, but holds water and increases weight slightly. Most good bags have nylon or polyester inner liners.

Outer shells are made of nylon, ripstop nylon, polyester, GoreTex, Dryloft, Versatec, or other proprietary microfibers designed to provide some degree of water and wind resistance. Nylon is the standard outer shell. It is light, strong, and the most breathable. No regular nylon, however, is better than mediocre for wind and water resistance. Ripstop nylon is stronger, more tear resistant, and also more wind and water resistant. Polyester is more resistant than nylon to degradation from UV radiation, and usually comes in microfiber formulations which are more wind and water resistant. Dryloft is a version of GoreTex specifically designed for sleeping-bag outer shells.

GoreTex and Dryloft sleeping bags are not waterproof--water easily leaks into the many seams. They are good for resisting moisture such as heavy dew, heavy breathing, and spilled drinks. Moreover, in real world conditions GoreTex and Dryloft sleeping bags are much warmer than conventionally-shelled ones because they are windproof. This can be important if you expect to be sleeping in the open or even in a breezy three-season tent. GoreTex and Dryloft add about two ounces (57 g.), and are only used in top-of-the-line bags that cost $300 or more, which is the sad end of this story.

Insulation Choices

Sleeping bag insulations produce loft between the inner and outer shells. Inside this loft the tiny fibers of the insulation (down or synthetic) create "dead" air space. This dead air space is what keeps the warm air warm, and the cold air out.

The latest crop of high tech synthetic insulations include Lite Loft, Thermolite Extreme, Primaloft, and Polarguard 3D. The two goose down insulations, available for millions of years, are grades: good quality 550 fill power and great quality 700 fill power.

The new synthetics are a vast improvement over the old Hollofil, Quallofil, and Polarguard. A good twenty-degree mummy with these new fills weighs about three pounds (1.35 kgs.) compared to four (1.8 kgs.) for the former. A comparable down bag weighs about 2.5 pounds (1.1 kgs.)

A three-pound, twenty-degree Lite Loft, Thermolite, Primaloft, or Polarguard 3D bag will stuff to about 8x15 inches, or 750 cubic inches (20x38 cm. or 12.5 liters). A similar down bag will stuff to 7x14 inches, or 500 cubic inches (18x36 cm. or 8.3 liters),  thereby saving 6x6x6 inches (3.6 liters) of pack volume.

The allure of synthetics is they maintain ninety percent of their insulating power when soaked with water. They simply don't retain much water, and dry quickly. Conversely, down loses ninety percent of its loft and warmth if soaked, and takes a very long time to dry.

Therefore it follows that wet down could lead to hypothermia and death at one extreme, and at minimum discomfort and aggravation. While I have carried a down bag through the tropics without incident, it was far from the ideal insulator since down absorbs moisture from humid air. On the other hand I didn't need much, if any, insulation, and found it easy to dry the slight dampness under occasional hotel room fans. The real danger comes in cold and rainy climates where everyone must be careful to keep down dry.

Hence synthetics are best for the tropics, cold and very damp areas such as southeastern Alaska and the Pacific Northwest, for river-running, and for hard hitchhikers who don't carry a tent or tarp.

Nevertheless down remains the most popular insulation among travel backpackers. It is still twenty percent lighter than the best synthetics, stuffs thirty percent smaller, feels luxurious, and is at least three times more durable. Moreover, most travelers are able to keep their down sleeping bags dry all the time. My nylon-shelled down bag has been damp a few times, but has never been wet except in a washing machine.

A good stuff sack is important, but note that stuff sacks with "dust flaps" are only water resistant, not waterproof. When traveling on or around water, lining your stuff sack with a plastic bag and sealing it should eliminate most risk. A well-sealed tent or bivy sack will keep rain from above away, although you should be careful not to pitch it in a low area where water could gather underneath.

How Much to Spend

In many hostels many backpackers leave their sleeping bags on their beds all day. I often do. And when I do, I'm glad my bag isn't a $500 GoreTex superbag. And when my pack is thrown on top of a bus and I don't see it again for a day, I'm also glad it isn't so valuable.

On the other hand the corollary to the Galton quotation heading this chapter is: If you don't sleep warm, you can't survive.

Care and Maintenance

Never dry-clean any sleeping bag. The risk is too great that a destructive solvent will be used, even if the clerk says they won't. Solvents and fumes may be retained in the insulation, producing skin irritation or an allergic reaction.

Don't put your sleeping bag in a top-loading, agitator washing machine. The agitator could damage it, internally if not externally. Instead, use a front-loading, heavy duty Laundromat machine that is usually dubbed "superwasher" or "doublewasher." These machines spin very fast, but they don't use an agitator. Use the warm setting and add a little gentle, easy-rinsing soap such as Woolite or Down Suds.

To dry, set the dryer temperature on low or medium and throw it in. High temperatures could be harmful.

Don't over wash your sleeping bag. Try spot washing for soiled areas. I wash my bag after several months of use.

Don't store a sleeping bag in its stuff sack longer than necessary. This quashes the loft of any bag. Soon after reaching a campsite, hostel, or hotel, I remove my bag and fluff it with a few shakes. At home I store it in a large cotton bag, which is supplied with most good bags.

Sleeping Bag Glossary

550 fill power down

Good quality down of which 1 ounce will loft to at least 550 cubic inches.

700 fill power down

Great quality down of which 1 ounce will loft to at least 700 cubic inches. Down ranges from 300 fill power to 800.

Lite Loft

Synthetic insulation from 3M. Made of tiny polyester/olefin fibers bonded with heat. Has a remarkably soft feel. A good alternative to down, and a popular quality synthetic.

Primaloft

Mixture of tiny and big fibers to duplicate the construction of down. Primaloft PL-1 is said to be the fastest drying synthetic, while Primaloft PL-2 is a less expensive (and less water resistant) version. A good choice for a synthetic.

Thermolite Extreme

New synthetic insulation from Dupont that replaces Microloft, and blends continuous filaments, heat-bonded fibers, and springy fibers. Probably a good choice.

 

Quallofil

Each fiber has seven holes to trap air. Stuffs well, but not known for durability. My Quallofil bag lost half its loft during three months of daily use. Not recommended.

Polarguard

Longest-lasting but huge-stuffing synthetic insulation. Not recommended for travel.

Polarguard HV (High Void)

The continuous polyester filaments of Polarguard have been hollowed 30% to reduce weight and bulk. Still too bulky to be ideal for travel, in my opinion.

 

Polarguard 3D

Newest Polarguard formulation of finer filaments that compresses better than Polarguard HV. Used by many manufacturers.

 

 

Hollofil 808, Hollofil 2

Cheap, heavy, and huge-stuffing insulations. Only useful for low-priced car-camping and backyard bags. Not recommended.

Dryloft

A version of GoreTex designed for sleeping bags. It has twice the breathability of regular GoreTex--thus insulation is less likely to become damp from perspiration under cold and damp conditions. Dryloft also makes a bag windproof.

Sculpted hood

Found on better mummies. Provides superior comfort and seal around your head as opposed to the more cheaply made flat hood pictured right.

#7 and #8 zippers

These are the most common sleeping bag nylon coil zipper sizes. Regardless of the manufacturer, two #7's or two #8's can usually be zipped together--though it may not be a heat-efficient combination. But then that isn't always the primary consideration.

Left zip/right zip

A sleeping bag with a zipper on the left side mates best with a right-zipped bag of the same model. If you usually sleep on your left side and/or write with your right hand, you may want a left-zippered bag. Right-sided sleepers and/or left-handed writers may want a right zip.

Stuff sack

Coated nylon sack for carrying sleeping bags. For canoe or flimsy bridge travel, line the inside with a plastic bag and seal tightly. Hydroseal makes waterproof stuff sacks. If the stuff sack is too small the daily stuffing ritual becomes aggravating and damages loft.

Illustrations: Campmor 20° F. mummy with sculpted hood and stuff sack.

Compression sack

A nylon stuff sack with webbing that reduces stuff size by thirty percent when cinched. Only recommended for an old, ugly bag you happen to have, since compression sacks permanently quash loft.

Down Suds

A gentle, easy-rinsing soap for down products. Woolite also works.

Sleeping Bags Compared

These are representative of the market--your local outdoor shop will have similar or newer models. Temperature ratings may not be exactly comparable from one brand to another. All measures are as claimed by the manufacturer.

Campmor +20º F Mummy (-8º C)

$100, 2 lbs. 4 oz. (1.02 kgs.) Mummy. 550 fill down with nylon inner and outer lining. Stuff sack: 7x14 in. (18x36 cm.) Cut wide at the shoulders (32 in., 81 cm.), but of average, slightly-constricting mummy-width from the knees on down. Not a great bag, but a good bag that has served well on my last four trips. My personal rating is about +30° F (-1º C).¹ (Pictured above.)

Campmor +45º Down Lite Tapered (+7º C)

$90, 2 lbs. (910 g.). Semi-rectangular. 550 fill down with nylon inner and outer lining. Stuff sack: 6.5x14 in. (17x36 cm.) Zip extends across the foot section allowing the bag to be opened into a comforter. A compact and light choice for fair-weather hostel-hoppers.

REI Thermo Pod +15º F (-10º C)

$140, 3 lbs. 10 oz. (1.65 kgs.) Mummy. Thermolite Extreme with nylon inner and outer lining. Stuff sack: 8x18 in. (20x46 cm.) Has 60% of insulation on top, 40% on bottom.

Eastern Mountain Sports MM +20º F (-8º C)

$190, 2 lbs. 10 oz. (1.19 kgs.) Mummy. 550 fill down with nylon inner and microfiber outer linings. Stuff sack: 7x14 in. (18x36 cm.) Microfiber on this bag resists moisture better than regular nylon.

The North Face Cat's Meow 3D Long +15º F (-10º C)

$160, 3 lbs. 2 oz. (1.42 kgs.) Mummy. Polarguard 3D insulation with water resistant microfiber inner and outer linings. Stuff sack: 9x17 in. (23x43 cm.) Long length model fits up to 6 ft. 5 in. (1.96 m.) tall.

The North Face Blue Kazoo +15º F (-10º C)

$210, 2 lbs. 7 oz. (1.11 kgs.) Mummy. 600 fill down with nylon inner and outer lining. Stuff sack: 7x13 in. (18x33 cm.) A top-selling bag for many years. Has a narrow cut for maximum warmth and minimum weight. Get in before you buy.

The North Face Foxfire DL +5º F (-15º C)

$420, 2 lbs. 14 oz. (1.30 kgs.) Mummy. 750 fill down with nylon inner and Dryloft outer shell. Stuff sack: 7x14 in. (18x36 cm.) Good for mild winter camping.

Western Mountaineering Apache +20º F (-8º C)

$255, 2 lbs. 2 oz. (964 g.). Mummy. 700 fill down with nylon inner and outer lining. Available in 5 ft. 6 in., 6 ft., and 6 ft. 6 in. sizes (1.67, 1.83, and 1.98 m.) Stuff sack: 7x14 in. (18x36 cm.) Western Mountaineering bags are prized by travelers worldwide. (Sometimes too prized--pictured right.)

Sierra Designs Rosa +15º F (-10º C)

$160, 2 lbs. 14 oz. (1.31 kgs.) Mummy. Polarguard 3D insulation with polyester inner lining and ripstop nylon shell. Stuff Sack: 9x19 in. (23x48 cm.) Regular model is sized for women to 5 ft. 5 in. (1.65 m.) tall, and has extra insulation for the feet.

Sierra Designs Joan of Arc 0º F (-18º C)

$170, 3 lbs. 14 oz. (1.77 kgs.) Mummy. Polarguard 3D insulation with polyester inner lining and ripstop nylon shell. Stuff sack: 11x21 in. (28x53 cm.) Has 7 in. (18 cm.) of loft, but 0° F rated synthetic insulations require enormous pack space.

Caribou Early Frost +20º F (-8º C)

$165, 3 lbs. 2 oz. (1.42 kgs.) Mummy. Primaloft insulation with nylon inner and outer lining. Stuff sack: 7x14 in. (18x36 cm.) 32 in. (81 cm.) width across chest.

Moonstone Minima XL +30º F (-1º C)

$210, 2 lbs. 1 oz. (935 g.). Mummy. Lite Loft with nylon inner and outer lining. Stuff sack: 7x14 in. (18x36 cm.) Has a relatively roomy cut across chest (31 in., 79 cm.) and is sized to fit travelers at 5 ft. 9 in. and 6 ft. 4 in. (1.75 and 1.93 m.) The Moonstone Optima XL is rated at 15º F (-10º C).

L.L. Bean Ultra Lite Loft +40º F (+5º C)

$90, 1 lb. 14 oz. (850 g.). Mummy. Lite Loft with nylon inner and outer lining. Stuff sack: 6.5x12 in. (16.5x30.5 cm.) This is a good bag for the tropics, hosteling, and summer desert hiking.

U.S. Army and NATO issue

Available for $10 to $20 in surplus stores, weight is around five pounds (2.27 kgs.) Heavy duty, but the insulation is likely to be worn-out, which is why they're surplus.

Sleeping Pads

The primary purpose of a sleeping pad isn't comfort, but insulation from Mother Earth so she doesn't suck all the heat out of you via conduction. When nighttime temperatures fall into the 50's and below (mid-teens for Celsius), camping travelers need a sleeping pad to overcome this powerful, heat-robbing effect.

For spring, summer, and fall travel two products stand out: Cascade Designs' Therm-A-Rest Staytek Lite and the GVG Pack-Mat Lite. These are open-cell foam pads with waterproof covers. Open the valve at one corner and within a minute or two they magically self-inflate. Both have twice the insulating power and are thicker and more comfortable than most closed-cell foam pads. You can blow in a few breaths to make it firmer and significantly increase insulation, or release air to make it softer.

Best of all, they roll-up small enough to fit inside your pack. Thicker and heavier models are available, but are unnecessary for spring, summer, and fall travel. For camping in winter conditions you can use a self-inflatable in conjunction with a full-length, 1/2 or 5/8 inch (1.25 or 1.6 cm.) closed cell foam pad.

Regular closed-cell foam pads are lighter and cheaper (about $10 and 12 oz. or 340 g.), but consume two to four times as much volume, thus requiring outside-the-pack lashing. After a few crowded buses and subways you'll be happy to have spent the extra money on a compact, self-inflating pad.

Photo: With a sleeping pad you'll be comfortable waiting for the train or enjoying the wide open.

 

Sleeping Pad Repair

If you cannot find a leak by sight or sound, fill the pad with air, close the valve, roll-up half the pad and place pressure there with your knees. Then pour water on the remaining portion to check for air bubbles. Repeat until the leak is found. Otherwise you'll need a tub. Repair with nylon tape or rubber cement.

Sleeping Pads Compared

Therm-A-Rest Ultra Lite II 3/4

$47, 14 oz. (397 g.) 47x20x1 in. (120x51x2.54 cm.)  Rolled size: 4x11 in. (10x28 cm.) Short length leaves the feet without insulation, but most users place clothes or their pack under their feet, if necessary. I have happily used the previous Ultralite 3/4 model for more than five years.

Therm-A-Rest Ultra Lite II Long

$60, 23 oz. (650 g.) 72x20x1 in. (183x51x2.54 cm.) Rolled size: 5.5x11 in. (14x28 cm.) Padding for your feet, if needed.

Therm-A-Rest Staytek Long

$62, 40 oz. (1.135 kgs.) 72x20x1.5 in. (183x51x3.8 cm.) Rolled size: 5.5x21 in. (14x53 cm.) It can also be rolled to about 8x11 in. (20x28 cm.) This thicker, full-length pad will go a long way toward keeping you warm while winter camping.

GVG Pack-Mat 3/4 Lite

$55, 13 oz. (368 g.) 47x20x0.8 in. (120x51x2 cm.) Rolled size: 4x11 in. (10x28 cm.) Has a non-slip polyurethane cover. This French pad is the lightest and smallest-packing self-inflator. Popular in Europe, but hard to find in the States.

GVG Pack-Mat Long

$65, 20 oz. (565 g.) 71x20x0.8 in. (180x51x2 cm.) Rolled size: 5x11 in. (13x28 cm.)

Generic closed cell foam pad

$6 to $16, 8 to 14 oz. (230 to 400 g.) Various lengths and widths, with thicknesses from 1/4 to 5/8 in. (0.6 to 1.6 cm.) Light and cheap, but not compact--all must be fastened outside your pack. If money is tight, take heart that many camping backpackers travel superbly with closed-cell pads. For summer try cutting a thin 1/4 or 3/8 inch pad to just what you need.

No pad

A pad isn't absolutely necessary for campers in hot climates like Greece and Spain in the summer, except for mountain areas.

Therm-A-Rest Repair Kit

$5, 1 oz. (28.35 g.) Contains adhesive, instructions, and patches for repairing pads, tents, sleeping bags, and jackets.

Vapor Barriers
Or,
What to do in face of butt-freezing cold and howling Jupitian wind

If for some reason you must spend a night at a temperature far below your sleeping bag's rating, a vapor barrier could save your life. First, put on all your clothes, but you must have good quality wicking fabrics next to your skin. Then get inside the large garbage bag you've been carrying for emergencies, and wriggle inside your sleeping bag in an area as wind-protected as possible. Pull the garbage bag tightly across your chest or neck so little air can escape. (Your head, of course, must always remain outside the garbage bag.)

This system dramatically reduces evaporative heat loss as your body adjusts to the high humidity micro-climate inside the plastic bag. The wicking action of your clothes prevents your skin from becoming damp and cold. However, if the layer next to your skin is cotton, water will not wick away and you may freeze to death from normal perspiration.

You can also line the inside of your sleeping bag with an aluminum space blanket, or pull bread bags over your feet. I used the space blanket/sleeping bag combination in late fall Germany and Czechoslovakia when overnight temperatures and synthetic loft simultaneously plummeted. Some mountaineers routinely employ vapor barriers since they add twenty to thirty degrees Fahrenheit of protection for almost no weight.

Notes

1. At 20° F  I would much prefer being snug in a four-season tent with one or more high-temperature females. back