The Sierra Designs Zissou Plus Three-Season Mummy Sleeping Bag has a traditional mummy shape, but with a quilt-style closure area that is integrated into the bag, to give it a more bed-like comfort. It intuitively adapts to varying temperatures, for true 3-season use.Traditional mummy shape. Unique integrated quilt: Dual zip and trapezoidal shaped quilt provides bed-like comfort in warm weather. Side wall baffles prevent down migration, keeping you warm. Anti-snag zippers. DriDown 700-fill duck down insulation stays dry 10-times longer than untreated down and dries 30% faster.