Should you invest in a winter sleeping bag?
Maybe not. If you have a dependable 15°F bag and plan only occasional winter trips, add a liner (see Sweet Dreams, below) and a foam pad (like the RidgeRest Classic, left) to bring your kit up to snuff for comfort in subzero temps.
Choose your temp rating. If the liner and pad upgrades aren’t cutting it, it’s time to look at a winter bag. Cold sleepers should go 10 to 20 degrees lower than the coldest conditions they expect to find. Warm sleepers should look only at bags with “gills” or full-length, venting zippers.
Should you buy a down or synthetic sleeping bag?
Synthetic bags can save money, but you’ll need a good sized pack (at least 60 liters) to carry one. Down weighs less and compresses better, but costs more (although buying duck down can reduce the price gap). If you’re planning an extended trip, hydrophobic treatments help keep down bags lofty by fighting moisture buildup on the feathers (a common problem even in dry weather, due to body moisture—you sweat while sleeping).