Ultra-light and technical, Sea to Summit's Flame™ Series bags are designed to keep you as warm as possible while minimising packed weight and size. The Flame™ 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. The women’s specific fit is wider at the hip and narrower at the shoulder and we’ve added extra down overall for increased warmth. Our 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 ULTRA-DRY Down™ protection also makes the Flame™ an impressive hard-alpine or adventure racing bag, where every gram is counted and down has never been a viable option