When the going gets tough, the tough dive inside the updated BTU -20 sleeping bag. Stuffed full with 800-fill hydrophobic DriDown insulation, the BTU -20 is made with a DriZone waterproof / breathable membrane for maximum warmth and comfort in even the coldest, wettest environments. This bag is also designed to hold up on the longest of expeditions utilizing a large #10 zipper that is 40 inches long, tuck stitch construction, and snag-free zipper tracks. Warmth is achieved via side-wall, box baffle construction, zipper draft tube, adjustable Expedition Jacket Hood, which fits as well as any hood on a down coat, and a fully corded draft collar with captured cord locks. Includes storage and compression stuff sacks. DriDown: Revolutionizing Down Insulation. Simply put, DriDown represents the evolution of down insulation. Regular down is treated with a molecular level polymer to create a hydrophobic finish on each individual down plume. This finish allows DriDown to stay dry 7-times longer, retain 34% more loft when exposed to moisture and humidity, and dry 33% faster than untreated down, keeping you warmer in any environment.