Lightweight but warm sleeping bags

Q. I need to get a good sleeping bag that weighs two pounds at most and will keep me warm in at least 30-degree weather. What kind of bag should I look for?
– Dylan the Undecided, St. Charles, Ill.

A. For cold-weather backpacking, I recommend a mummy-style bag. The cut is narrow so there’s less empty space for your body to heat up. Mummies are also lighter than traditional rectangular-shape bags and are easily compressible to a size that’ll fit inside your backpack.

Most mummy bags are made with either synthetic insulation or tons of down feathers, usually from geese or ducks. While down bags are warm, lightweight and compressible, if they get wet they’ll quickly lose their insulating ability and won’t keep you warm. Synthetic insulation will continue to keep you warm even when it gets wet. Best of all, synthetic bags are usually more affordable.

Here are some options:

BSA 100th Anniversary Sleeping Bag ($90, www.scoutstuff.org) Made by Eureka to honor the BSA centennial, this 30-degree bag filled with ThermaShield synthetic insulation weighs in at a mere 2 lbs. 5 oz.

REI Polar Pod +25 ($89, www.rei.com) A no-frills synthetic mummy that weighs 3 lbs. 12 oz.