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. Fortunately, shopping for a backpacking bag is now easier than ever thanks to the EN temperature rating standard.
The 3 Key Factors:
We're always happy to talk about sleeping bag
construction and comfort features, but a bag purchase can really be boiled down to these 3 elements:
Choose a bag rated for the coldest temperature you expect to encounter. Thanks to the EN standard, described below, this rating is a highly reliable and accurate measurement.
Weight vs. roominess
When backpacking, you want to keep weight low without jeopardizing comfort or safety. For some, low weight overrides all other concerns (comfort, durability, convenience, price). For others, weight is less important than having a roomy bag for a good night's sleep. Most bags try to strike a balance between these extremes.
Type of insulation
Your main purchasing decision is between the types of fill: down, synthetic and the new DriDown™. Goose-down fills 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. DriDown is goose down treated to resist moisture, the Achilles heel of regular down.
Sleeping bag ratings underwent a revolution in recent years. Traditionally, a sleeping bag's temperature (or "comfort") rating has pegged the lowest temperature at which the bag will keep the average sleeper warm. In this traditional approach, a bag labeled a "20-degree bag" has been one intended to keep most sleepers comfortable if the air temperature drops no lower than 20°F.
Are these ratings infallible? No. All humans have different metabolic rates. Women, on average, have been scientifically proven to sleep colder than men. What's more, the U.S. outdoor gear industry has never had a standard method to determine temperature ratings. Many manufacturers assign ratings based on their own research. Therefore, these ratings have best served as a guide, not a guarantee.
Consistent Ratings: EN Methodology
Enter the European Norm (EN) 13537 testing methodology. This testing protocol, already in European use for several years, was adopted in 2009 by sleeping bag manufacturers seeking more reliable temperature ratings for their 3-season backpacking bags. (Most other manufacturers have since followed suit.) EN testing is performed in independent (third party), internationally certified laboratories to ensure sleeping bags are subject to a standardized test.
The result? EN methodology produces temperature ratings you can trust and compare head-to-head with the EN ratings on other brands' bags. If you know the temperature range you'll encounter on your overnight trip, you can compare EN-rated bags and confidently choose the one that will best ensure a comfortable night's sleep.
EN Ratings Explained
EN 13537 testing reflects the scientific determination that women sleep colder than men given the same sleeping bag in the same outside temperature. So you'll see separate temperature ratings and terms used for each gender.
To communicate this, the tag of each EN-rated sleeping bag includes the following temperature ratings:
- EN Comfort Rating (for Women): The lowest outside air temperature at which a standard woman can sleep comfortably in this bag.
- EN Lower Limit Rating (for Men): The lowest outside air temperature at which a standard man can sleep comfortably in this bag.
Keep in mind that EN ratings are based on a sleeper wearing one base layer and a hat, and using an insulating sleeping pad under the bag.
Bottom line? If you're a woman, look for the EN "Comfort" rating to decide if the bag will meet your needs. If you're a man, check the EN "Lower Limit" temperature to see if the bag is right for you.
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, but rather to keep a woman alive. It is not advisable to be too literal about the "Extreme" temperature rating.
How EN Bag Testing Is Done
For EN 13537 temperature tests, a full-size mannequin with heaters and temperature sensors is dressed in 1 layer of long underwear and a hat. It is placed inside the sleeping bag being tested. The bag is laid atop an insulating sleeping pad inside a climate-controlled chamber. The mannequin is heated to simulate body warmth and measurements are taken of the air in the climate chamber and the "skin" surface of the mannequin. From these measurements, the insulation value of the sleeping bag is calculated. These calculations provide the 3 EN ratings described above.
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 as well as adding cushioning. On some bags, the pad replaces the need for insulation on the bottom side of the bag. If sleeping on snow or frozen ground, we recommend using 2 pads.
- Tent: Using a tent or bivy sack traps a layer of dead air around you, warming it by up to 10°F.
- Metabolism: You might be a "cold sleeper" who prefers extra insulation when sleeping. Or maybe you are a "warm sleeper" who kicks off the covers at home.
- Gender: Women generally prefer slightly warmer bags than men.
- Clothing: What you wear inside the bag makes a difference. 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 colder-than-expected nights, a fleece jacket and pants can help.
- 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?
that display EN ratings can be expected to provide comfort to the temperature stated on the bag, keeping in mind the variables described above.
For non-EN-rated bags, select a bag with a comfort rating that is a bit lower than the lowest temperature you expect to experience. For example, if near-freezing temperatures can be expected, then choose a 20°F bag instead of a 35°F bag.
For any sleeping bag, you can always vent it on warmer nights by using the double-zipper to open the area by your legs. Or, simply drape the unzipped bag over you.
Here's a general rule of thumb on how sleeping bags are categorized:
Summer Season = +35° and higher
3-Season Bag = +10° to +35°
Cold Weather = -10° to +10°
Winter/Extreme = -10° and lower
In the last decade or so, sleeping bag options for women have increased dramatically. These bags are specifically designed and engineered to match a woman's contours. When compared to men's bags, women-specific bags
usually have the following characteristics:
- Shorter in length
- Narrower at the shoulders
- Wider proportionally at the hips
- Occasionally, 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 instead 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.
is the fluffy plumage that forms the undercoat of geese and ducks. This natural fiber is an extraordinary insulator. Premium down usually comes from geese, as their plumes offer a higher fill power. Fill power (or loftiness) refers to the number of cubic inches 1 ounce of down will displace. The higher the down's fill power, the less down is needed to achieve a given temperature rating. For example, a +10°F bag using 800-fill-power down will weigh less than a +10°F bag using 600-fill-power down. Because high-fill-power down is less plentiful, it usually comes with a higher price tag.
Down loses its insulating properties when wet, so any high-quality down bag will use a shell fabric treated with a durable water repellent (DWR) finish. DWR allows water to bead up rather than soak through the fabric. In addition to DWR, a few specialty bags feature a waterproof/breathable coating so the bag can be used in wet climates.
A new water-resistant down, called DriDown™, was introduced in spring 2012. Though it sounds almost too good to be true, molecular-level treatment can be applied to down to give it water-resisting properties without adding weight or affecting its insulating abilities. Sierra Designs was the first bag-maker market bags using its version of treated down.
(usually a type of polyester) retain much of their warmth even when wet, so they are a good choice in damp climates. They are quick-drying, nonallergenic and (in high-end bags) almost as light as down bags.
The downside is that a synthetic bag offers a little less warmth for its weight, plus 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. These feature short strands of fine-denier filaments that 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 DriDown bag if you want superior warmth, compressibility and durability. Though initially more expensive, down's superior durability makes it a good value over the long haul. You might want to avoid down (except DriDown) if you camp mostly in damp, rainy climates.
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 lofty and more durable. Synthetic fills are usually the better choice for wet climates.
The Basics of Heat Loss
Sleeping bags keep you warm by trapping and holding a layer of "dead" (non-circulating) air next to your body. The dead 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 and stay warm.
The key 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 and vice-versa). Sleeping bag insulations try to minimize equilibrium by retaining your body heat.
There are 4 main types of heat loss that bags guard against.
- Convective heat loss is by far the primary culprit. This 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 amount of loss is less significant than convective heat loss 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). This heat travels as waves through the air and is best absorbed and radiated by smaller-diameter plumules or fibers (approximately 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 the backcountry sleeper, this primarily refers to your body's contact with the cold ground. An insulating foam sleeping pad offers your best defense against conductive 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, even though your damp garments may not initially feel cold. In extreme cold conditions (which are very dry due to cold air not being able to hold moisture), you should consider a vapor barrier liner or vapor barrier clothing. These can limit the cooling caused by evaporative heat loss and reduce the water needed to stay hydrated, but may feel clammy at warmer temperatures.
Sleeping bag designers must balance the ideals of loft, compressibility and weight when considering how to address these heat-loss issues.
Sleeping Bag Construction
Shape and Fit
The shape of a bag certainly affects your sleeping comfort. All true backpacking bags are mummy-shaped, but some roomier camping bags can double for use in the backcountry (these tapered bags are usually categorized as semirectangular bags). To compare sizes, look for the shoulder and hip girth specs provided on product pages or the in-store sleeping bag info guide.
Rules of thumb:
- For maximum thermal efficiency and less weight, choose a mummy bag with narrower shoulder/hip specs. Some folks, 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 larger shoulder/hip specs or semirectangular bags for greater comfort. These bags are a bit bulkier and heavier, though.
Baffles, Shingles and Layers
Between a bag's outer shell and inner lining, its insulation can be held in place by several techniques. Down bags use a system of baffles. Synthetic bags use either a network of shingles or a layered approach. The goal of these construction techniques is to ensure an even distribution of insulating fill to avoid cold spots.
Down bags typically use the following baffle constructions:
- Box: This time-tested approach is strong and keeps down from shifting so you enjoy consistent warmth. Common variations are trapezoidal and slant boxes, which are used most often in the footbox area since the 3-dimensional design requires a shape other than a parallel sided box.
- 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 this 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. The top layer is sewn to the shell, and the bottom is sewn to the lining. 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 is a less expensive construction and 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. Any high-quality down bag—and many synthetic-fill bags as well—feature a shell fabric treated with a durable water repellent (DWR) finish. DWR is an unseen barrier that allows 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.
|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"
Other Bag Features
Zipper compatibility: Many backpacking bags can be zipped together for sleeping by couples. Just be aware that mating 2 bags creates bigger 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 refers to a proprietary REI design technique that 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, so check it out to see if it works for your needs.
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.
Trapezoidal footbox: This design creates added 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. A secondary benefit is that the extra space reduces the tension your feet put on the bag, which helps improve longevity of the insulation.
Sleeping Bag Liners
Sold separately, a sleeping bag liner
is primarily used to help keep your mummy bag clean and thus make it last longer. (Note: Rectangular sleeping bag liners are commonly called "travel sheets.") A bag liner also adds anywhere from 5° to 15°F of extra warmth to your sleeping bag, depending on the liner material. In hot climates, you can use a bag liner or travel sheet by itself and forgo the sleeping bag.
You typically have a variety of bag-liner material choices:
- Silk: Very lightweight (about 5 oz.). Silk helps insulate in cold weather but is absorbent and breathable in warm weather. Price: moderate to expensive.
- Cotton: Strong, durable and absorbent, but not the lightest or most compact. Price: economical.
- Fleece and microfleece: Warmer (adds up to 12°F) and a bit heavier choices. Fleece is soft, moisture-wicking and quick-drying, but the mid- and heavyweight varieties tend to be bulky. Price: moderate.
- Synthetics (CoolMax and MTS®): Moisture-wicking and breathable, which makes these great for humid conditions. Has a bit of stretch, too. Price: moderate.
- Insulated (Thermolite Reactor Extreme): This adds up to a claimed 25°F of warmth thanks to its hollow-core fiber insulation. It also dries 50% faster than cotton. Price: moderate to expensive.
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. Most sleeping bags now incorporate pad loops to help secure your sleeping bag to your sleeping pad.
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.
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.