The three-season, 800-down filled REI Igneo is one of the best sleeping bags a weight-watching backpacker can carry. Rated to 19 degrees, the one-pound, 15-ounce bag stays warm in freezing temps, but breathes incredibly well on even the hottest days, so its innards don't become balmy. A water-resistant shell deflects the wet stuff, while the bag's unique insulation system keeps 60 percent of the down fill on the top half, where you need it most. It's cut comfortably snug around the chest, yet doesn't feel constrictive. Amazingly, it packs down to the size of a softball. [$329; rei.com]