Have you run across the term “down fill power” while shopping for sleeping bags, puffer jackets, or a duvet? These numbers range from 450 to 900, and sometimes above. Generally—but not always—the ...

Dollar for ounce, no part of an ultralight backpacker’s kit is more costly to cut down on weight than the sleep system. Premium down — we’re talking 800 or even 900 fill power — costs exponentially ...