Western's warmest bag at -40° F; windproof and highly water-resistant.

　　Denali, Aconcagua, the Himalaya... mountaineering in the extreme. These are places where the margin for error is zero, and so the Western Mountaineering Bison Gore Infinium sleeping bag is most often chosen to serve. A full Gore Infinium shell makes this bag windproof and virtually waterproof while remaining lightweight and surprisingly compressible. Stuffed with over 40 ounces of 850+ fill down, the Bison has 10 massive inches of heat-trapping loft. Huge V-Block Side Baffles and horizontal baffles across your chest keep the down fill in place, and double Interlocking Draft Tubes and a down-filled Gore Infinium collar seal in heat while howling winds surround your tent. The huge hood is not only well-filled but is completely made with Gore Infinium and has a large ruff to seal your face from the elements. The Bison is the crowning glory of Western Mountaineering and demonstrates their commitment to innovation and quality. This life-saving bundle weighs in under 5 lbs and is the warmest bag you'll find anywhere.

　　Like all of Western Mountaineering's bags, the Bison down sleeping bag is made by hand in San Jose, California. Their down is sourced from free-range mother geese who are never live-plucked or force-fed.

　　The GORE-TEX INFINIUM™ WINDSTOPPER® series enhances quality and performance, combining versatile aspects of support and comfort without the need for total waterproof protection. Durable water resistance combined with increased breathability, better packability, and optimized lightweight elements are the defining features of this technology. GORE-TEX INFINIUM™ WINDSTOPPER® is totally windproof and provides highly water-resistant protection for unstoppable performance.