The American Bison has amazing fiber. The coat of the bison contains several different types of fiber. The main coat is made up of coarse fibers called guard hairs, and the downy undercoat (average 18.5 microns). The undercoat is shed annually and consists of fine, soft fibers which are very warm and protect the animal from harsh winter conditions. This fiber is the hardest for us to process as it is quite short, often less than 1 inch, and the guard hairs can be quite fine, but still stiff and scratchy in the finished product.