Two natural fibers, yak wool and wool, share the knit of the Turtle Fur Yak Wool Sienna Beanie in equal parts. Machine knitting joins them into a yak wool beanie for winter days. What Our Gearhead(R) Experts Are Saying:"On early starts, scraping the car in the dark, the yak wool knit and fleece lining kept my head comfortable until the heater caught up."