How to Choose a Sleeping Bag

(page reprinted from


How Do Sleeping Bags Work?

Comfort Rating

Down or Synthetic Insulation?

Which is Right for You?


On a cool evening in an unfamiliar place, a good sleeping bag seems to work like magic. Slip inside one after a few post-sundown shivers have rattled your body and, within minutes, the chill in your bones is replaced by a warm glow. It's a sweet sensation that assures you of a comfortable night's sleep.


Here are some tips to help you make a smart choice when selecting your own sleeping bag:

  1. Match your bag's comfort rating with the coldest nighttime temperatures you expect to encounter—and maybe even exceed that number for little security.

  2. Bags using down insulation are lighter (providing a higher "warmth-tp-weight" ratio) than bags using synthetic fill. They also compress into smaller shapes and last longer.

  3. Synthetic-fill bags can provide some insulation even when wet, and they dry out fairly quickly. Plus, for the same temperature rating, they cost less than down bags.

  4. A bag's shape matters. Mummy-style bags insulate most effectively and are your best choice for colder, high-elevation conditions; rectangular bags give you more room to change sleeping positions but offer more space that your body must heat up.

  5. A good sleeping pad is essential. Your body weight compresses a bag's insulation when you lie on it, so you need a reliable buffer between, your bag and the cold ground.

How Do Sleeping Bags Work?


Sleeping bags keep you warm by trapping and holding a layer of "dead" (non-circulating) air next to your body. This air, which is warmed by your body heat, forms a barrier between you and colder air or cold surfaces.

When evaluating bags, consider these key factors:

Comfort Rating


A sleeping bag's temperature or "comfort" rating identifies the most extreme temperature the bag is designed to accommodate. When you hear a bag described as a "+20 bag," it suggests most users should remain comfortable if the air temperature drops no lower than 20 degrees Fahrenheit.

Are such ratings infallible? No. Humans all have different metabolic rates, and no industry standards exist that uniformly determine sleeping bag comfort ratings. Instead, each manufacturer assigns a rating to its bags based on its own research. Therefore, use these numbers as a guide, not a guarantee. If you have trouble deciding between two bags, it's not a bad idea to select one that offers a little more warmth than you think you might need.


Many factors affect your ability to keep warm inside a sleeping bag:


Even experienced campers and backpackers can be surprised by unexpectedly cold overnight conditions, particularly during trips in the spring and fall. It's smart to be prepared.

Tip—To be ready for those extra chilly nights, select a bag with a temperature rating that slightly exceeds the low end of the temperature range you expect to experience. If a +20° F bag sounds right for you, a +10° bag would probably work well, too. On warm nights, you can always vent a bag (by using the double zipper to open the area near your legs) or simply drape it over you, unzipped. It never hurts to be a little over-prepared.

Recognizing that comfort ratings are merely general guides, REI organizes sleeping bags in the following categories:


Bag Type Comfort Rating (°F)
Summer Season  +35° and higher
3-Season Bag  +10° to +35°
Cold Weather -10° to +10°
Winter/Extreme  -10° and lower


Please note: Even in summer, a +35° bag may leave you feeling chilly when sleeping in the high country. If you think of yourself exclusively as a warm-weather camper, yet plan to routinely camp at higher elevations (3,000 feet and up), choose a bag with a comfort rating at least in the 20s.


Down or Synthetic Insulation?


The insulation or "fill" inside a sleeping bag largely determines a sleeping bag's:


Down is the wispy, fluffy undercoating found just beneath the outer feathers of geese and ducks. This natural fiber is an extraordinary insulator. Goose down is preferred to down from ducks, prized because it is believed its plumes offer a higher "fillpower" (explained below).

Down's positives include:

Down, though, does have a downside:

Down is graded according to fill power—meaning the number of cubic inches one ounce of down will displace. The down’s volume is measured in relation to its weight (the volume of an American/Imperial ounce (28.35 g) in cubic inches (cuin). This gives us the so-called fillpower. No measurements are taken for down only sleeping bags. Summer and camping sleeping bags have approximately 350 cuin fillpower, good quality bags have 500 cuin, superior quality bags +600 cuin and truly top quality bags +700 cuin.


Synthetic Materials

Synthetic materials are basically plastic threads (extruded polymers, to be technical). The threads are most commonly a continuous filament (a long, single strand). They can also be arranged in short "staples" up to four inches long. Usually the threads are hollow, reducing their weight and enabling them to trap more air.

The advantages of synthetic fill include:

Which one is right for you?

Down works well for just about everyone except people who frequently find themselves in rainy conditions.

Synthetic insulation is a good choice for kids and newcomers to camping and backpacking. It costs less than down and dries out relatively quickly if it gets wet.

Many women's bags are cut to accommodate a woman's body shape and preference for extra insulation.

Down always wins in terms of weight, compressibility, warmth and durability. Yet the value and performance of synthetic bags makes them very popular. Synthetic bags are improving each new model year, and they're champs when rain is a threat or cost is a factor.

What about length? Do you need a "regular" or "long" model? The general rule is as follows: If you are no taller than 6 feet, choose a "regular" length bag. If you are up to 6-feet-6, you want a "long" bag.


Back to Hiking Back Home


Last update 16/04/2007