Merino Wool is a natural fiber that's incredibly soft, moisture-wicking, and will keep you warm in the winter and breezy-cool in the summer. We also took this super yarn and blended it with a little bit of polyester and spandex to help perfect the fit of every pair, and create the built-in arch support so many feet now know and love. Women's Merino Wool Blend Calf Sock 4-Pack - Neutral Mix - Small - Bombas