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.