Choosing a Sleeping Bag

Shells

Tallac Stormlight: 600-fill down and a soft, quiet, water-resistant, windproof, breathable shell

There is no universal consensus on the best fabric. Often bags will have a tightly woven synthetic shell with a DWR (Durable Water Repellent) finish. The higher the thread count of the fabric, the better the water and wind resistance. Check the entire bag for leaking fill, which is a sign that the fabric might not have a sufficiently tight weave.Shells run the gamut from simple, smooth polyester/nylon taffeta to waterproof Gore-Tex. The majority of sleeping bags available have outer shells made from tightly woven polyester or nylon micro fiber that tends to be supple, light, and somewhat water and wind resistant. Ripstop is also another strong shell contender, mainly because the nylon/polyester is extremely durable. A smaller percentage of bags are made with Gore-Tex or Dry Loft shells. Gore-Tex is usually not recommended because it doesn't breathe sufficiently to allow moisture to escape to the outside of the bag. Dry Loft, also made by Gore, is more breathable and more highly water-resistant than most microfibers.

Fills

Down or synthetic, that is the question. For most first-time buyers, whether to invest in a fluffy goose down bag or a less expensive one filled with man-made fibers is a real dilemma. Insulative materials are sandwiched between the shell and lining fabrics using a variety of methods (enclosed channels, layers, baffles). Check on how the fill is distributed throughout the bag. Shake the bag, and make sure the fill stays in place. Insufficient baffles, channels or layers can allow the fill to migrate away from your body, compromising the integrity of the bag and its ability to keep you warm.

If you're car camping or relying on strong Sherpa shoulders, synthetic bags are a good choice. They do tend to be heavier and much bulkier than a down bag of comparable warmth, but they don't lose their loft over time, and require as much maintenance, such as airing out after each use to avoid dampness. Synthetic bags also retain much of their warmth, even after taking a soaking.

However, if you want to go light, with a small pack, down is your best choice. It's the Cadillac of bag fill, with a higher weight-to-warmth ratio than any synthetic fill on the market. But get down wet, and you're due for a cold night. Down also takes much longer to dry than synthetic fiber.

Synthetic fills come in many forms and a bewildering variety of brand names. The technology behind them keeps getting better and better, yielding fibers much closer in weight, warmth, and compressibility to down than ever before. For the best performance, look for sleeping bags stuffed with Lite Loft, Polarguard 3D, Thermolite Extreme, and PrimaLoft Sport (formerly PrimaLoft 2).

Fiber manufacturers vary certain fiber characteristics to improve the thermal performance of a batting (increase its insulation per unit weight). They can vary the fiber diameter (denier), fiber length (from short staple lengths to long, continuous filaments), the shape of the fiber cross section, fiber crimp, and the size and shape of holes or voids inside the fiber. Batting producers can vary the thickness, density, and weight of the fiberfill also. Down bags will each have a fill power number. The number indicates how much space an ounce of down can fill. The higher the fill power, the loftier and warmer the bag.