When you need more protection, our Extreme Gear line is lightweight, warm and durable. Stay warm and comfortable under the harshest circumstances. 90% Bison down and 10% Nylon, this is our highest Bison blend line. Combed from the insulating, downy undercoat of the American Bison, until you put these on, it's hard to believe their ultra-soft comfort and lightweight warmth. Bison Down is harvested from buffalo in Colorado and South Dakota then finely knit for maximum warmth with minimum bulk.