For a small amount of weight, a sleeping bag allows you to stay warm and comfortable despite the chill (or perhaps bitter cold) of a backcountry night.

This article helps you choose the best sleeping bag for backpacking. Not a backpacker? Read the REI Expert Advice article, Sleeping Bags for Camping.

The 3 Key Factors

A sleeping bag purchase can be boiled down to these 3 elements:

  • Temperature rating: Choose a bag rated for the coldest temperature you expect to encounter. The rating is sometimes part of the bag's name, such as the Marmot Plasma 15 bag (rated to a temperature of +15°F). Thanks to the EN standard, described below, this rating is now a reliable measurement.
  • Weight vs. roominess: When backpacking, you want to keep weight low without jeopardizing comfort or safety. For some, low weight overrides other concerns (durability, convenience, price). For others, weight is less important than having a roomy bag for a good night's sleep. Most bags seek to strike a balance between these ideals.
  • Type of insulation: Your choices are down, synthetic or the newer water-repellent down. Down fills (either goose or duck) are very light, compressible, durable and breathable. While initially more expensive, they offer great long-term value. Synthetic fills excel in damp, cold conditions and have less sticker shock up front. They are slightly heavier and less compressible than down. Water-repellent down (e.g., DriDownTM) is down treated to resist moisture, the Achilles heel of regular down.

Shop REI's selection of sleeping bags.

For a closer look at EN ratings and what makes a bag comfortable, read on.

EN Temperature Ratings

Sleeping bag ratings underwent a revolution a few years back. Traditionally, a bag's "comfort rating" pegged the lowest temperature at which the bag would keep an average sleeper warm. Thus, a "20-degree bag" was intended for air temperatures no lower than 20°F.

Were these ratings infallible? No. Humans have varying metabolic rates. Women, on average, have been scientifically proven to sleep colder than men. Furthermore, the U.S. outdoor gear industry had never adopted a standard to determine such ratings, so manufacturers assigned ratings based on their own research. Temperature ratings were at best a guide, not a guarantee.

Consistent Ratings: EN Methodology

Enter the European Norm (EN) 13537 testing protocol. EN has been adopted by REI and most other sleeping bag manufacturers for their 3-season backpacking bags. Why? It is internationally accepted as the most objective and dependable standard available.

Here's an example of the EN tag you'll find on all REI-brand 3-season backpacking bags:

EN sleeping bag tag

EN Ratings Explained

EN bag testing

In EN testing, a bag is assigned 2 temperature ratings:

  • Comfort rating (for women) is the lowest temperature at which the bag will keep the average woman warm.
  • Lower-limit rating (for men) is the lowest temperature at which the bag will keep a man, on average, warm.

As noted earlier, the dual ratings reflect the fact that women typically sleep colder than men. Thus, a bag's comfort rating will always be higher, often significantly, that its lower-limit rating.

For example, the REI Radiant sleeping bag carries an EN lower-limit rating of +19°F and a comfort rating of 32°F. This indicates that an average woman would remain comfortable in the bag as long as the air temperature falls no longer than 32°F.

EN ratings are based on a sleeper wearing 1 long underwear layer and a hat, and sleeping on a single 1"-thick insulating pad.

An EN extreme rating is also provided. It essentially describes a worst-case scenario. The bag isn't designed to keep anyone cozy in such low temperatures; it's a survival-only rating for the average adult woman. It is advisable not to be too literal about the "Extreme" rating.

What Else Affects My Overall Warmth?

Besides a sleeping bag, these factors influence your warmth and comfort:

  • Sleeping pad: This insulates the space beneath your bag and adds cushioning. On the bottom side of some bags, the pad actually replaces the insulation. If sleeping on snow or frozen ground, we recommend using 2 pads.
  • Tent: Using a tent or bivy sack traps a layer of air around you, warming it by up to 10°F.
  • Metabolism: You might be a "cold sleeper" who prefers extra insulation. Or maybe you are a "warm sleeper" who kicks off the covers at home.
  • Gender: Women generally prefer slightly warmer bags than men.
  • Clothing: Long underwear and clean socks help insulate you while also keeping body oils off of your bag. A cap and neck gaiter help retain body heat. For cold nights, wear a fleece jacket and pants.
  • Hood: Sleeping bags with hoods can be cinched up on cold nights to help retain warmth.
  • Hydration: Staying hydrated increases your likelihood of sleeping warm. A warm drink before bed is a popular tip.

What Temperature Rating Should I Choose?

EN-rated sleeping bags can be expected to provide comfort to the given temperature, keeping in mind the variables described above.

For non-EN-rated bags, go with a comfort rating lower than the lowest temperature you expect. For example, if near-freezing temps are expected, bring a 20°F bag instead of a 35°F bag.

Tip: You can always use the double-zippers on warm nights to vent an area by your legs. Or, simply drape the unzipped bag over you.

Sleeping bags are generally categorized like this:

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

Women's Bags

Bag shape by gender

Women-specific bags are designed and engineered to fit a woman's contours. When compared to men's bags, this means:

  • Shorter in length
  • Narrower at the shoulders
  • Wider at the hips
  • Often, extra insulation in the upper body and/or footbox

Insulation: Down or Synthetic?

Sleeping bag insulation (or "fill") doesn't provide any warmth by itself; it works to minimize the amount of heat your body loses while sleeping. We explain more about the principles of heat loss below.

Two basic insulation types are commonly used—down and synthetic—with water-repellent down fast becoming a popular third choice.

Down (Goose or Duck)

Down is the plumage that forms the undercoating of waterfowl. It forms in plumules and consists of fluffy, wispy filaments. It is an exceptional insulator, prized for being light, easy to compress, long-lasting and breathable. It excels in cold, dry conditions or whenever saving weight and space are priorities.

Down is more expensive than synthetic fill, but it maintains its loft (which provides its heat-trapping ability) at a near-original state longer than synthetics. That makes down a good value over the long haul.

Duck down has recently gained broad acceptance for use in outdoor gear due to advances in down processing techniques and availability. Goose down has recently become more scarce, which has significantly driven up its price.

Fill power is the term used to measure down's ability to loft, and thus trap heat. It is calculated by how many cubic inches 1 oz. of down can fill in a testing device.

Higher-grade down, taken from more mature birds, requires fewer plumules to fill space and achieve a certain temperature rating. So any bag rated +20°F with 700-fill-power down, no matter if its fill is duck or goose down, will be lighter than a +20°F bag using 600-fill-power down.

If you place a pair of 600-fill-power sleeping bags side by side—one using duck down and one using goose down—their loft, weight and compressibility will have little or no variance. Fill power is fill power.

Where duck and goose down can potentially differ:

  • Top-end fill power: Duck down can achieve fill-power ratings no higher than 750 or 800. Premium goose down can reach 900 and potentially even higher ratings, but it’s quite expensive.
  • Durability: Goose plumules are typically larger than duck plumules and can potentially retain their lofting ability for a longer time. One manufacturer estimates the average lifespan of a goose down bag (at its original temperature rating) is 25 years vs. 20 years for a duck down bag.
  • Odor: Modern processing/cleaning techniques have reduced the possibility that duck down, when wet, can exude a gamey smell. It is conceivable, however, that people with a heightened sense of smell may still detect a slight odor from duck down no matter how clean or dry duck down is.

Many major bag-makers have made the transition to duck down throughout their product lines. Testing, EN ratings and and performance standards should be the same no matter which fill is used.

Water-repellent Down

Moisture is the chief nemesis of down. Wet down becomes matted and flat, losing its ability to retain heat.

New proprietary technologies (e.g., DownTek and DriDown) treat down at a microscopic level with a water-repellent application, allowing the filaments to resist light moisture without compromising loft.

Manufacturer testing indicates down with a water-repellent treatment can withstand dampness created inside a bag through body vapor. The technologies are also believed to help damp down dry out faster and minimize (or perhaps eliminate) any odor caused when down gets wet.

If dunked in a stream or exposed to heavy rain, even treated down will get wet. Remember, it is water-repellent, not waterproof.

The cost of treating down minimally affects the price of bags, adding up to $20 to their cost.

No standardized tests have been established for gauging the effectiveness water-repellent down. Manufacturers use their own tests to self-confirm the merits of the technologies.


Synthetic insulation (usually a type of polyester) is less expensive than down and dries considerably faster. They are nonallergenic and retain much of their warmth even when wet. They are a good choice in damp climates and for beginning, casual or budget-minded backpackers.

The downsides are that a synthetic bag offers a little less warmth for its weight, is a bit bulkier when compressed and its insulating power gets reduced each time it is stuffed into a stuff sack.

There is a long list of competing brand names for synthetic insulations, which can make shopping confusing. A more relevant distinction is knowing whether a synthetic insulator is short-staple or a continuous filament.

Short-staple fills (e.g., PrimaLoft®) are the predominate choice. Their short strands of fine-denier filaments are densely packed to minimize heat loss. This makes these bags feel soft and flexible, much like a down bag, and allows for great compressibility. They are, however, a bit less durable.

Continuous-filament fills (e.g., Climashield®) use a thicker continuous filament that is lofty, strong and durable. They have a stiffer feel and are less compressible than short-staple bags.

Which Insulation Is Right for You?

Choose a down or water-repellent down bag if you want superior warmth, compressibility and durability. Though initially more expensive, down's superior durability makes it a good long-term value.

Choose a synthetic bag if you want both good performance and a lower price tag. Short-staple synthetic bags offer excellent compressibility, while continuous-filament synthetic bags are more durable. Synthetic fills are usually the better choice for wet climates.

The Basics of Heat Loss

Basics of Heat Loss

Sleeping bags keep you warm by trapping and holding a layer of "dead" (non-circulating) air next to your body. This air is warmed by your radiated body heat, with the bag forming a barrier between this air and the colder ground or outside air. The less air space there is to heat, the faster you warm up.

The concept behind this is equilibrium: Nature always seeks to balance temperature differences (e.g., hot objects in a cool room will cool to room temperature). Insulations minimize equilibrium by retaining your body heat.

There are 4 main types of heat loss that bags guard against.

  • Convective heat loss is the primary culprit. It refers to heat lost through air currents. Bags minimize this by using a complex tangle of insulation strands or plumules to block air trying to escape from your body to the cooler outside air. Dense filaments of larger diameter fibers (approximately 3 denier) block these most effectively.
  • Radiant heat loss relates to heat dissipating away from your body. This loss is less significant and depends on the difference in temperature between 2 visibly adjacent surfaces (e.g., from your skin to the bag's inner shell, or from the bag's inner shell to the insulation inside). Radiant heat travels as waves through the air and is best absorbed and radiated by smaller-diameter plumules or fibers (about 1 denier) and fill that is white in color.
  • Conductive heat loss refers to objects of different temperatures that are in direct contact with each other. For backcountry sleepers, this means your body's contact with the cold ground. An insulating sleeping pad offers your best defense against this heat loss.
  • Evaporative heat loss is the chill caused by moisture transforming from a liquid to a vapor. You have undoubtedly felt the cooling of wet skin as evaporation occurs. Similarly, you should always change from sweaty clothing to clean, dry clothing when getting into your sleeping bag. In extreme cold conditions, consider a vapor barrier liner or vapor barrier clothing. These can limit the cooling caused by evaporative heat loss, but may feel clammy at warmer temperatures.

Sleeping bag designers balance the ideals of loft, compressibility and weight when considering how to address heat-loss issues.

Sleeping Bag Construction

Shape and Fit

The shape of a bag also affects your sleeping comfort. All true backpacking bags are mummy-shaped, though some semirectangular bags are suitable for the backcountry. Shop by comparing the shoulder and hip girth specs provided on product pages.

Some guidance:

  • For maximum thermal efficiency and less weight, choose a mummy bag with narrow shoulder/hip specs. You may, however, find it hard to get comfortable in these more restrictive bags.
  • If you have a broad frame or are a restless sleeper, consider mummy bags with wide shoulder/hip specs or a semirectangular bag. These bags offer more comfort but are a bit bulkier and heavier.

Baffles, Shingles and Layers

Insulation can be held between a bag's outer shell and inner lining by several techniques. Down bags use a system of baffles; synthetic bags use either a network of shingles or a layered approach. The goal is always to ensure an even distribution of insulation.

Down bags typically use the following baffle constructions:

Box baffles and Slant box baffles

  • Box: This durable approach keeps down from shifting so you enjoy consistent warmth. Variations include trapezoidal and slant boxes, which are often used in the footbox.


  • Sewn-through: This weight-saving technique is used on ultralight bags as their lesser amounts of insulation preclude the need for a baffle. The downside is that it can allow cold spots at the stitched areas.

Synthetic bags typically use one of these constructions:


  • Shingles: Shingles are cut pieces or sheets of fill stitched to both the shell and lining. They overlap each other somewhat like the shingles on a house.


  • Layered: Most popular is the offset-quilt approach. This features 2 layers of continuous insulation offset to reduce cold air penetrating the quilted seams. Simple, but effective. Another version, known as quilted-through, is a sheet of insulation cut to fit the shape of the bag. The shell, insulation and lining are all sewn together with a single stitch line. This less-expensive technique is used only on warm-weather bags since it is prone to cold spots.

Shell and Lining

The outer shell of a sleeping bag is typically made of a ripstop nylon or polyester for durability. The shells of most high-quality bags are treated with a durable water repellent (DWR) finish. DWR causes water to bead up rather than soak through the fabric

The inside lining of a sleeping bag, on the other hand, should promote the dispersal of body moisture, so DWR is not used here.

Tip: How can you tell if a shell has a durable water repellent (DWR) treatment? Rub a wet cloth across the surface of a bag. If the water beads up, then it has DWR.

Bag Length

Men's Women's
Short: For people up to 5'6" Regular: For women up to 5'6"
Regular: For people 5'7" to 6'0" Long: For women 5'7" to 6'0"
Long: For people 6'1" to 6'6"  

Note: The North Face offers a few X-Long bags for campers up to 6'8".

Other Bag Features

Zipper compatibility: Many backpacking bags can be zipped together for sleeping by couples. Just know that mating 2 bags creates gaps inside, so it's a less efficient way to stay warm. You can mate any 2 sleeping bags IF:

  • One bag has a "right-hand" zipper and the other a "left-hand" zipper. A right-hand zipper means the bag opens and closes to your right when you are lying in the bag on your back.
  • The zippers are the same size. Most brands use either a size #5 or #8 zipper, so these sizes need to match.
  • The length of the zippers is compatible. Some bags have 1/2-length zippers, others use 3/4-length zippers. You can still zip together bags with different zipper lengths, but you may have cold spots where the zippers don't match up.

It's also OK to mate bags of differing comfort ratings. You can arrange it so the warmer bag covers the colder sleeper.

Hood: You can lose a significant amount of heat through your head, so virtually all backpacking bags include a built-in hood. When cinched with a drawcord, a hood prevents heat from radiating away. Some hoods offer a pillow pocket that you can stuff with your clothing to create a pillow.

Draft tube: This is an insulation-filled tube that runs alongside the bag's main zipper. It's designed to keep warmth from escaping between the zipper coils.

Draft collar: Usually found on bags rated 0°F or colder, these are insulated tubes positioned just above the shoulders to prevent body heat from radiating up and out of a bag.


In the round: This proprietary REI design technique creates 3-dimensional "sides" to a sleeping bag. These vertical baffles, shingles or layers help provide efficient warmth to a bag's head, side and foot sections.

Stash pocket: This keeps small items, such as your MP3 player, watch or glasses, close at hand. Pocket locations can vary by model.

Pad loops: These sewn-in straps provide an attachment point so you can secure your sleeping pad directly to your sleeping bag so you won't roll off.

Footbox comparison

Trapezoidal footbox: This design adds space in the foot area to allow a more natural sleeping position for your feet. This is most useful if you sleep on your back rather than on your sides. The extra space also reduces the tension your feet put on the bag, which improve longevity of the insulation.

Sleeping Bag Liners

Sleeping bag liner

Sold separately, a bag liner is primarily used to help keep your mummy bag clean and thus make it last longer.

For shopping help, see the REI Expert Advice article, Sleeping Bag Liners: How to Choose.

Sleeping Bag FAQs

Q. Does a sleeping bag's comfort rating decrease with use?

A. Yes. Bag makers generally agree that a sleeping bag will lose some of its warmth over time. The exact amount lost depends on how often the bag is used and how well it is stored.

Q. Is this loss of insulation equally true for down and synthetic fills?

A. No. Down plumules break down at a much slower rate than do synthetic fibers. In fact, down bags are known to last for 20 to 30 years if cared for properly. Synthetics are made from either short staples or continuous strands of fill. The continuous-filament variety is the stronger and more durable of the two, especially if its used in a shingle construction. Again, the proper use and storage of any bag are also important factors in its durability.

Q. Why do fills eventually lose the ability to insulate after being compressed?

A. Compression can cause synthetic fibers to actually break in half—think of them as spaghetti noodles—and the broken strands lose the ability to trap air and keep you warm. The feathers in down bags are more resistant to breakage, but they too will break down if stored tightly under prolonged pressure.

Q. How do I keep from rolling off my sleeping pad at night?

A. Many sleeping bags incorporate pad loops to help secure your sleeping bag to your sleeping pad. One bag maker, Big Agnes, uses a pad sleeve instead of pad loops to accomplish the same thing.

Q. Is there a right way to stuff your bag into its stuff sack?

A. Not really, but it's a bit more efficient if you start with the foot end of the bag first. This allows air to escape through the top opening and not be trapped when you are compressing the bag.

Q. Can a compression stuff sack be used with any sleeping bag?

A. Yes, this type of stuff sack works wonders to compress either a down or synthetic sleeping bag to its minimum size for more efficient packing. Never use a compression stuff sack for long-term bag storage.

Q. How do I clean my sleeping bag?

A. For tips, read our separate discussion of sleeping bag care.

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Contributors: Linda Ellingsen, outdoors writer; Tom Kimmet, REI product manager; David Mydans, REI Gear & Apparel designer; Mary Klueber, REI Seattle camping specialist; Kelly Huffman, REI Expert Advice writer.