Climbing or traversing technical pitches with a massive load dangling behind you is a bad way to go through life. Western Mountaineering created the Alpinlite 20-Degree Down Sleeping Bag for alpine climbers and weight-obsessed backpackers who demand top-shelf quality and bottom-line weight savings. Its 850-fill down insulation boasts some of the highest quality loft-to-weight ratio around, meaning it's surprisingly warm for how little it weighs. Western Mountaineering wrapped this insulation around a highly breathable shell to keep the down light and lofty when you're sleeping in a tent under a rainstorm.