Additional comfort and insulation is given by a 3 dimensional mummy shape. By redesigning the traditional mummy shape to include additional high integrity fibers in the sidewalls we have created a shape that gives extra space where you need it without increasing weight and bulkiness. This is the closest you can get to high quality down performance with all the advantages of a synthetic filling. The filling, evolutionary design and quality makes this a unique range of fiber filled bags. The Blizzard sleeping bags also have our unique inside closing of the hood opening and opening for both arms. The zipper is positioned away from the ground. This reduces heat loss and the zipper is more accessible for opening and closing.