Our all natural yak crew high socks are made from 70% yak, 25% nylon, and 5% spandex. Nylon and spandex are added for increased durability and shape retention. Yak is perfect for socks because it is extremely soft and warmer than merino wool. Yak fibers are hollow which makes it a better insulator than sheep’s wool. These are made with a terry construction, which provides extra cushion for your walking and hiking pleasure. Being knit from a natural fiber, these socks wick away moisture, keeping skin dry and cozy. This special wicking ability keeps you warm in winter and cool in summer. As with all our socks, these are made in our sock mill on our Pennsylvania farm. Our socks are designed by a podiatrist to assure you receive the best design for comfort and foot health. Care instructions- Machine or hand wash in cold water, air dry.