Big Agnes - Lulu 15-Degree Sleeping Bag (Integrity), Purple/Dark Purple Insotect Tubic is a revolutionary tubular insulation system engineered to provide the maximum cubic loft for supreme thermal efficiency and user comfort. Through its innovative design and construction, Insotect Tubic delivers performance benefits that make gear significantly loftier, warmer & more durable. Superior thermal efficiency - the significant air space created by the DualVault and Vertical Thermal Channel delivers the best thermal efficiency. Built in pillow pocket holds a fleece or Big Agnes Pillow No-draft collar seals around neck to keep cold air from sneaking in Lining: Soft, breathable nylon taffeta with stain resistant finish The pioneers of mtnGLO technology