Ultra-light and technical, the Sea to Summit Spark™ Series bags are designed to keep you as warm as possible while minimising packed weight and size.The Spark™ Series spans everything from an ultralight liner to an expedition weight mid-winter bag. While the end usage is very different, they reflect a design ethos of matching weather conditions to the lightest bag possible.The secret to the impressive performance is a combination of premium materials and careful design. The RDS 850+ Loft premium goose down, light-gauge #3 YKK zip and high performance 10D Nylon shell and 7D lining fabrics, set the stage for superior performance. These materials are combined with a contoured mummy design for efficient insulation, and that mummy design is then tweaked for each model to best fit the use scenario.ULTRA-DRY Down™ water-repellent treatment protects the down from external moisture and condensation from the inside of the bag, virtually eliminating the negative effects moisture has on down. All Sea to Summit Down Sleeping Bags use Responsible Down Standard (RDS) certified down. The ULTRADRY Down™ protection also makes the Spark™ an impressive hard-alpine or adventure racing bag, where every gram is counted and down has never been a viable option. Features Ultralight 7D and 10D fabrics for minimal weight and packed sizeRDS 850+ Loft Premium Goose ULTRA-DRY Down™ for maximum insulation value Contoured mummy shape for comfort and efficient insulation Vertical chest baffles prevent down migration and cold spots Sewn through construction minimises weight Sewn through vertical baffles on chest optimises position of down to prevent it moving during use ½ zip with single slider aids access while keeping weight to a minimum Updated sizing provides extra room for both shoulders and hips while still maintaining insulation efficiency Includes lightweight Ultra-Sil™ Nano compression bag for compact storage Shell: 100% Nylon, Lining: 100% Nylon, Primary Filling Material: GOOSE DOWN (Min. 90% Down), Stuffsack: 100% Nylon excluding Trims Sea to Summit Spark I SP1 Down 5°C Sleeping Bag