The Zenbivy Bed's patented 2-piece design is the first hybrid backpacking sleeping bag of its kind to match the warmth-to-weight ratio of a mummy bag while completely eliminating constriction. The separate top quilt adds incredible versatility and the fitted sheet means no more sliding off the mattress. Combined, the quilt and sheet create a complete sleeping "bag" that is just as warm and light as a mummy sleeping bag but a whole lot more comfortable.