Compared to wool, bison down is warmer, better for moisture control, more durable and easier to care for. The major challenges of using bison down are its short staple (length of fiber) and exorbitant cost - some of the reasons why you dont see it used more often. Despite the challenges, United By Blue has pent the last year developing the yarn and have now created a sock that is technically sound, commercially viable, and fully made in America. Flat toe seam, reinforced heel, and padding for support. 56% Merino Wool, 24% Bison Down, 18% Nylon, 2% Spandex. Made in USA. Small: Women 6-10 / Men 5-9.