Gear Reviews

Sierra Designs BTU -20

An Arctic-worthy 800-fill down mummy.

Brand: Sierra Designs

Model: BTU -20



4lbs. 2oz.

It could have been a gear-tester horror story—an open-air bivy, between snowdrifts, on a 0°F night in New Hampshire’s White Mountains. But this Arctic-worthy 800-fill down mummy kept our tester off the evening news. “I was warm and comfortable all night, even though the clothes I slept in were sweat-soaked from the day’s hike,” our guinea pig reports. “I usually have trouble keeping my feet warm in winter, but the microfleece-lined footbox eliminated that problem.”

When he awoke, the bag’s exterior was caked in ice, but it dried after 20 minutes in the sun. The extra warmth and superior weatherproofing, thanks to a Drizone waterproof/breathable shell, make this -20°F bag worth the money and weight for hikers who camp in deep-winter conditions: It’s like an insurance policy against bad weather. The cut is efficiently trim, reports our thin, 165-pound tester, but not confining, and the weight-shaving, jacket-style hood fits closely—big guys and restless sleepers should try it in the store. The BTU packs down small compared to similarly warm winter bags (9”x19”) in the included compression sack, and for the weight, few bags deliver more warmth. $529; 4 lbs. 2 oz.; -20°F;


If you don’t camp in temps below 0°F, and don’t need a waterproof shell, get the Mountain Hardwear Phantom 0°. A thread count exceeding 400 per inch makes the 800-fill down bag luxuriously silky, and testers loved the superfat draft collar. (“Warm as a mink stole,” says one). $475; 2 lbs. 10 oz.; 0°F;
Great for cold weather camping, the BTU -20 has a jacket style hood for maximum heat retention and a microfleece lined foot box for extra warmth and comfort. A Funk Off treatment on the liner keeps this bag smelling fresh on long backcountry trips.