Rated to 15 degrees Fahrenheit, the Big Agnes Lost Ranger Sleeping Bag packs to two-thirds the size of comparable down bags. Down is the lightest, most packable, and most efficient insulation available. Big Agnes makes sleeping bags without insulation on their bottoms because down compressed by your weight loses virtually all of its insulating value. Instead, Big Agnes puts a sleeve in the bag floor into which you slide your sleeping mat. This system offers several major advantages: 1) The sleeping pad provides more warmth than compressed insulation. 2) You're guaranteed never to roll off your pad in the middle of the night. 3) You can stuff the lightweight bag and pad together for compact packing. *Compatible with any 20in wide rectangular sleep pad.