The Big Agnes Cinnabar Series -40 degrees Sleeping Bag is one of the warmest bags you can buy. Big Agnes built this expedition bag for adventures like summiting 8,000m peaks or self-supported missions across Antarctica. Insulated with 850 fill power DownTek water-repellent down inside a super-light, high-strength nylon ripstop shell with specialized body-mapped thermally efficient baffles, this Bag will keep you warm in some seriously nasty conditions. An ergonomic footbox adds space and extra insulation around your feet for better sleep, and an internal mesh stash pocket keeps everything important close at hand. Rated warm down to -40 degreesF Expedition-style bag for summiting 8,000m peaks or self-supported missions across Antarctica Premium 850 fill power DownTek water-repellent down insulation Superlight, high tear strength shell with PFAS-free waterproof coating Body-mapped, thermally efficient baffles Specialized fit designed for sleeping in layers and changing inside the bag Baffle shape maximizes loft while keeping liner and heat close to the body Side-access zipper on opposite side of full zipper for quick-access and heat retention Internal mesh stash pocket for phones and small necessities Insulated tube along upper hood opening seals out drafts when cinched Oversized draft collar with adjustability 3D anti-snag draft tube prevents heat loss along the zipper Ergonomic footbox with increased insulation Interior bottom of footbox features polyester taffeta fabric with a moisture-wicking finish for durability and moisture management Low-profile cordlock lets you un-cinch the hood with one hand Left zip, 70 inch YKK #5 anti-snag locking zipper for a smooth, quick zip Zipper garage Interior fabric loops for sleeping bag liners Streamlined exterior loops for hang drying or storage