The Spark Ultralight Mummy Sleeping Bag Series spans everything from an ultralight down-filled liner, to a mid-winter fast-and-light sleeping bag. Each model uses premium materials and no-frills design to provide cutting-edge performance. Ultralight does not mean ultra-tight: The Spark mummy sleeping bags are snug but still have adequate wiggle room for the performance-oriented, backcountry user. Features ULTRA-DRY Down 850+ Loft 90% Down Cluster Premium Goose Down certified Responsible Down Standard (RDS) 10D shell and 7D liner materials help to achieve the incredible lightweight and compact packed size Includes lightweight Ultra-Sil compression bag and storage cell Zipper-length trimmed for gram-saving performance: 50AdegF, 40AdegF, and 28AdegF have 1/3-length zippers 18AdegF and 5AdegF have full-length side zippers Baffle construction: 50AdegF and 40AdegF have sewn-through construction 28AdegF has baffles in the torso and sewn through in the leg area 18AdegF and 5AdegF are fully baffled