Denali, Aconcagua, Himalaya… mountaineering in its extreme sense. These are places where mistakes cannot be made and so the Bison is most often chosen to serve. Gore Windstopper fabric makes this bag impervious to the elements while remaining lightweight and very compressible. Crammed with 42 ounces of 850 fill power down this bag has 10 abundant inches of heat trapping loft. Huge V-Block Side Baffles and horizontal baffles across your chest keep the down fill in place. Double Interlocking Draft Tubes and a down filled Gore Windstopper collar seal in heat and security while howling winds surround your tent. The massive hood is not only well filled but is completely made with Gore Windstopper fabric and has a large integral hood ruff to seal your face from the elements. The Bison is the crowning glory of Western Mountaineering and demonstrates our commitment to innovation and quality. This life saving bundle weighs in at a scant 4 lb. 10 oz.