EmailReviews recommend considering the following features when choosing a sleeping bag:
- Goose down gives the most loft (and insulating power) for its weight, compresses the most for backpacking and keeps its loft longest. It's also softer and adapts to temperature changes. Its drawbacks include price, the fact that it also loses insulating power when wet and that some people are allergic to down. Reviews say the best synthetic fill is now Climashield, but Polarguard Delta and the softer Primaloft Sport outperform Polarguard 3D, which in turn outperforms Hollofil and Quallofil. Reviews say that Thermolite filling is only found in the cheapest sleeping bags and provides minimal warmth.
- Give the zipper a good workout. Nothing is worse, in the middle of the night, than struggling to unsnag a zipper in the dark. The best sleeping bags have stiffeners in the zipper draft tubes to minimize this problem.
- A full-length two-way zipper is best for a three-season bag. This means that you can unzip just part of the bag -- at the foot or legs, for example -- to ventilate areas that might get too warm otherwise.
- Choose a bag shape that fits your sleeping style. If you sleep on your back, a trapezoidal foot box allows your feet to stick up naturally. If you sleep on your side or move around a lot in your sleep, a stretch bag will be more comfortable, and one that secures to the sleeping pad will keep the sleeping bag securely on the pad. If you feel utterly claustrophobic in a mummy bag, even one that stretches, then try a modified mummy bag. You may even decide that the extra weight of a rectangular bag is worth carrying.
- Look for fit that's close without being tight. For maximum warmth, a sleeping bag should drape comfortably close to all parts of your body, with no big air gaps to waste your body heat. On the other hand, if a sleeping bag is too tight somewhere, you won't be comfortable in it. Most sleeping bag specifications include the girth at the shoulders, hips and feet, but experts say it's best to try different sleeping bags in person if at all possible. Women's sleeping bags are narrower in the shoulders than men's sleeping bags. They are also wider in the hips and usually have extra insulation at the feet and chest.
- The hood should fit comfortably. If you use a pillow, make sure there's room for it. Some bags have drawstrings that are too long and get in your face; others have Velcro that can catch in your hair and make noise that bothers tent mates. Be sure you can keep snug and warm without feeling claustrophobic.
- A watch pocket is handy. This little pocket for an LED light or watch is becoming a standard feature on the best sleeping bags. Both professional and user reviews say it seems indispensable once you've had one.
- A wearable bag adds versatility. This means that the foot area can be unzipped so you can walk around while wearing the bag. On a cold morning or evening, you can wear the bag sitting up, or to heat water for tea.
- Check the bag's loft. Press the bag down and see if it springs back up quickly. If not, you will probably have loft problems later.
- Gently pull the inside of the bag away from the outer covering. If you hear small tearing sounds, you can be sure the baffles are not going to hold up for long, and you'll end up with a bag that has all its insulation clumped into one place.
- A sleeping bag liner or special sleeping clothes keep a bag cleaner longer. This is more important for down sleeping bags than for bags with synthetic filling that can be washed in a front-loading washer. Down bags should be kept as clean as possible inside, because cleaning them is tricky -- best done professionally. Changing into a separate set of clean clothes, or using a silk or other lightweight sleeping bag liner, will delay the need for this.
Reviews can help in estimating the lowest temperature rating at which a sleeping bag will feel warm, but they're only a rough guide. Experts say that attempts to standardize ratings across brands have failed, so they're most useful in comparing sleeping bags from the same company. Some people "sleep cold" and shiver in sleeping bags which other people find quite warm. Women usually sleep colder than men, so many reviews suggest that women pick a sleeping bag rated about 10 degrees colder than the lowest temperature they think they'll encounter. Some sleeping bags are designed specifically for women, narrower in the shoulder area but roomy around the hips, with extra insulation especially at the feet.