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 7Denier 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 Ideal for mid-summer fast hikes or adventure racing Sewn through quilted construction to minimise weight and keep down in position Doubles as a liner to significantly boost the warmth of a second bag Includes removable stuff sack attached to footbox for compact storage 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 10°C Sleeping Bag