A sleeping bag is a pretty simple piece of gear, but there are several factors you should keep in mind when selecting one. After all, a bag that might be perfectly adequate for a summertime backyard slumber party could be completely inadequate for camping in sub-freezing temperatures. By the same token, spending a summer night in a cold-weather bag can make you feel like a burrito fresh from the microwave.
Sleeping bags almost always come with a comfort rating. Most three-season bags, for example, will have a comfort rating somewhere between 15 and 50° Fahrenheit. Some companies assign comfort ratings through a scientific test known as the EN (European Norm) 13537, which involves a mannequin fitted with sensors, wearing long underwear and socks, lying in a sleeping bag in a cold room. Along with a comfort rating, EN-tested bags often come with an “extreme” rating, which purports to show the coldest temperature in which the bag will protect you from injury or death from the cold. Not all sleeping bag brands use EN testing; some commission tests of their own, while others seem to make an estimate based on experience. However they are derived, comfort and extreme ratings should be considered a guide, not a guarantee. When camping in cold weather, it’s best to err on the side of caution. For example, if the temperature is likely to get down to freezing (32°F), use a bag that is comfort-rated for 20°F, just to be in the safe side.
Mummy or Rectangle?
Sleeping bags come in two basic shapes: rectangular and mummy. Rectangular bags such as the Slumberjack Country Squire are generally roomier, which is a blessing for bigger people and sleepers who tend to change positions often during the night. They also tend to be bulkier and heavier, even the ones rated for mild weather, since they use more material than the narrower mummy bags; this makes them more popular with car-campers, whereas backpackers are always looking to save space and weight. Mummy-style sleeping bags are more form-fitting, and some people find them downright restrictive. Their design, however, makes them inherently warmer: there’s less “dead” air inside a mummy bag to be warmed by your body heat. Many mummy bags also come with hoods, which cover the head and offer additional protection against the cold.
If you expect to transport your sleeping bag in a vehicle and use it in mild weather, a rectangular bag should be fine. If you’re backpacking, or car camping in the spring or fall (or even in the summer at high elevations), consider a mummy-style bag.
Shell and Lining
The shell refers to a sleeping bag’s outside fabric, and the lining is the fabric on the inside. Modern sleeping bags tend to be made of nylon or polyester, which are durable and lightweight. If cold weather is likely, you will be more comfortable inside these synthetic fabrics than in cotton, which is notorious for trapping perspiration, which leads to a chill, although for warm-weather camping or indoor use in sleepovers, many people enjoy cotton or poly/cotton flannel. Some bags, such as the Snugpak Special Forces, have durable water-repellent treatments on their shells. Most sleeping bags are used inside tents, which should prevent you from being rained on, but condensation inside a tent can be significant, so a Durable Water Repellent (DWR) treated fabric is something to keep in mind. Still, waterproof sleeping bags are relatively rare.
A quick note about DWR: DWR is a factory-applied fabric treatment that makes material water resistant, while maintaining its breathability. It is often given a rating, like 1800 mm DWR. This means a tube pressed to the fabric can be filled with water to a height of 1800mm (just under 6') before any water seeps through. DWR coatings can wear off over time, but spray-on products are available to restore it.
Goose down is widely considered the warmest kind of sleeping bag insulation. It’s also lightweight and compressible, making it attractive for backpackers. Many winter campers, who rely on their gear to be safe, as well as comfortable, will use nothing else. But down is also expensive, and it has a serious operational drawback: it’s all but useless if it gets wet—and it takes a long time to dry. Some sleeping bags, like the Kelty Cosmic line, use goose down that is chemically treated to be water resistant, retaining the “loft” or fluffiness that is the key to effective insulation.
Most people use sleeping bags with synthetic insulation. Often made of polyester fibers, synthetic fill can insulate even when wet and it dries out more quickly than down bags. Bags with synthetic fill are easier to clean, and they pose no problems for people with allergies. While they don’t pack down into a tight roll as readily as a down bag and they tend to be heavier, if there’s a chance of a soaking (and it seems there always is) many find that good synthetic insulation is worth the extra weight and bulk.
Not to be confused with the lining (the fabric on the inside of a bag), a liner is a mini-sleeping bag made of a single thickness of cotton, polyester, silk, or other fabric. Its main purpose is to keep the inside of your bag cleaner and prolong its life; a liner can usually be tossed in the laundry like a bed sheet. But using a liner can also make a sleeping bag several degrees warmer, and since they don’t take up much room or add much weight, they’re easy to slip into a pack in case the weather forecast (or you) is looking optimistic. Finally, a liner can be used alone for camping in hot climates, when you’d like to sleep inside something but don’t want an insulated bag.
Offset, Sewn-Through, and Baffles
How a sleeping bag is sewn can affect its performance. Bags for mild-weather use often feature sewn-through or quilted construction, where the shell and lining, with the fill sandwiched between, are simply sewn together. When sleeping in the cold, these stitching lines can leak a lot of heat. Higher-end bags rated for cold weather often feature offset construction, with a layer of insulation sewn to the shell and another sewn to the liner, with the stitch lines staggered. This eliminates heat-leaking stitches and the cold spots that result. Baffles are generally used in down bags, to keep the feathers evenly distributed throughout the insulation space. They’re vertical walls between the shell and lining. Some down bags have what are known as continuous baffles; think of a series of tubes wrapping around the sleeper. These allow you to shift the down where you want it—usually to the underside, to make the top side more comfortable in warm conditions.
You could say a zipper is the only difference between a sleeping bag and a comforter folded in half lengthwise. But good sleeping bags have zippers that can be used to regulate your sleep temperature. Two-way zippers, for example, can be opened at the bottom of the bag as well as the top, to provide a little ventilation for your feet. Some sleeping bag makers include a separate zipper across the foot box (the part of the bag where your feet go) for this purpose. At the other end of the temperature spectrum, better bags will have a simple locking mechanism at the head end of the bag to prevent the zipper from being inadvertently opened during the night.
Better cold-weather bags are built with an insulated sleeve that seals the zipper, preventing cold drafts from seeping in between the zipper’s teeth. Some also have what’s known as a “draft collar,” a similar tube that prevents heat loss through the head opening and preserves warmth for your core. Draft tubes and collars can make the difference between a cold, restless night and a comfortable restful sleep.
Almost every sleeping bag comes with a small sack to stuff it in after you’ve rolled it up. A sack with compression straps makes it easy to squeeze the bag into a tight, neat bundle that takes up less space inside your pack. Some bags come with stuff sacks with soft fleece linings—turn the bag inside out, stuff it with a fleece top or other clothing, and it becomes a nice pillow. Whatever kind of stuff sack comes with your bag, however, don’t use it for storage between camping trips; the extended compression will damage the bag insulation’s loft that is so important for keeping you warm. Instead, fold the sleeping bag loosely and store it in a large plastic bag or pillow case, or drape it over the bar in a closet if you have the space.
You Need a Pad, too
No matter how plush your bag may seem, you should still invest in a sleeping pad to cushion your body from the hard ground and help keep you warm. The latter point is so important that many sleeping pad makers assign R-values to their products, just like the insulation in a house. Pad styles include simple textured sheets of closed-cell foam (the Therm-a-Rest Z Lite and Z Lite Sol are beloved by many backpackers for their lightness, affordability and virtual indestructibility); self-inflating mattresses, with a core of foam that expands to its original size when unrolled and can be firmed up with additional air from an inflation vent; and air mattresses, which must be blown up but are the most portable option and, some say, the most comfortable.
There’s a sleeping bag for every sleeper, situation, and budget. Give some thought to how you’ll be using your bag and choose accordingly. After all, resting comfortably at night always leads to having more fun the next day.