The North Face The One Sleeping Bag is the one and only bag with an innovative 3-in-1 interchangeable system for the widest temperature rating across the market. Three separate layers zip together for a comfort rating of 29F. The bag also zips the outer and bottom layer together for a comfort rating of 46F, and the midlayer can zip into the bottom without the outer layer for a moderate rating around 35F. The North Face insulated the midlayer with light, lofty 800-fill down, and the outer layer is synthetic to maintain warmth in wetter climates. As if that weren't enough versatility, the bottom layer can roll up to double as a pillow.