The Sea to Summit Alpine™ Series Sleeping Bag combines their most technical sleeping bag features to deliver reliable performance while cocooning you in the highest quality RDS 850+ Loft Goose ULTRA-DRY Down™. Designed for high altitude mountaineering and arctic conditions, the contoured mummy design delivers efficient insulation, while our updated expedition sizing provides space for extra clothing to be worn inside the bag. The anatomically shaped and oversized footbox can comfortably accommodate boots when necessary. Vertical baffles over the chest section ensure the down insulation cannot migrate or shift to the outside of the bag during sleep, creating cold spots. A side block baffle construction maintains the 60/40 fill ratio, keeping more down on the top of the bag for maximum insulation. 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 Free-Flow Zip system provides a half zip on the right side of the bag to provide freedom of movement for both arms as well as additional ventilation. The full length, two-way left side zip provides easy access and extra ventilation options. Sea to Summit's waterproof yet breathable NanoShell™ fabric provides protection from wind and moisture. The tightly sized and carefully panelled hood fits snugly around your head, allowing you to maintain maximum warmth with minimal adjustment. An oversized zipper draft tube is fitted with the lightest and stiffest anti-snag materials for effortless operation and to prevent heat loss through the zipper. Features  Designed for extreme cold and high-altitude conditions Contoured mummy shape for efficient insulation Expedition sizing for extra space and layered clothing Vertical chest baffles prevent down migration and cold spots Side block baffle with 60/40 fill ratio keeps more down on the top of the bag for maximum insulation Anatomically shaped and oversized footbox can accommodate boots Free-flow half right-side zip for freedom of movement and additional ventilation RDS 850+ Loft Premium Goose ULTRA-DRY Down™ for maximum insulation value Waterproof/breathable NanoShell™ fabric protects against wind and moisture Snug panelled hood maintains maximum warmth with minimal adjustment Oversized draft tube with anti-snag materials, prevents heat loss through zipper Oversized neck draft tube with a dual adjustment system for even cinching and maximum warmth YKK #5 side zip has two sliders for easy access and extra ventilation Large internal security pocket EN13537 Temperature Rating: The EN13537 is a European standard for sleeping bags that provides three temperature levels to help guide you when choosing a bag: Comfort: The temperature at which a standard woman can expect to sleep comfortably in a relaxed position. If you are female or consider yourself a cold sleeper, use this rating to decide the coldest temperature the sleeping bag is suitable for. We emphasise the Comfort temperature for our women’s specific sleeping bags. Lower Limit: The temperature at which a standard man can sleep for eight hours in a curled position without waking. If you consider yourself a warm sleeper, use this rating to decide the coldest temperature the sleeping bag is suitable for. We emphasise the Lower Limit temperature for all our unisex sleeping bags. Extreme: This is a survival only rating for a standard woman. Between the lower limit and the extreme rating a strong sensation of cold must be expected and there is a risk of health damage due to hypothermia. This is an extreme survival rating only; we do not recommend you rely on this rating for normal use. Free Flow Zip System: The Free-Flow triple-zip design ensures your sleeping bag retains maximum warmth and efficiency when needed and multiple ventilation options when it’s not. The half zip on the left side of the bag provides freedom of movement for both arms, additional ventilation and also means the top third of the bag can be folded down as a mini quilt. The full length, two-way right side zip and separate foot zip transforms the bag into a full quilt for when the mercury climbs higher than expected. 850+Loft Down: 850+ Fill Power indicates that 1 oz of down will re-expand to over 850 cubic inches after compression. Higher loft means that less down can be used to achieve the same temperature rating – important for performance sleeping bags. The loft and down quality/composition are independently tested by the International Down and Feather Laboratory (IDFL) – a copy of the certification is supplied with every Sea to Summit sleeping bag. Ultra-Dry Down: ULTRA-DRY Down™ is a permanent nano-level water repellent polymer treatment applied to our down which protects it from external moisture and condensation from inside the bag virtually eliminating the negative effects moisture has on down. RDS Certified Down: All Sea to Summit sleeping bags use only down which is certified according to the Responsible Down Standard. The RDS is helping shift the entire down and feather industry towards more humane animal rearing and handling practices.Overseen by the industry leading Textile Exchange, the RDS requires independent, third-party assessments of all aspects of animal rearing and handling throughout the entire supply chain. By using only down that meets the audited requirements of the RDS, we can have confidence that each phase of the collection process has been completed with the welfare and ethical treatment of waterfowl in mind.To learn more about RDS, visit responsibledown.org Sea to Summit Alpine III ApIII Down Sleeping Bag, -40°C High Altitude