Every material we use in these socks has been carefully chosen and tested to meet our rigorous durability standards. We currently use natural and synthetic fibers, and only 3 types of fiber per sock. As you'd expect, Ullerware are actively investigating and testing new fibers and yarn blends that do not appear in current products. Ullerware prioritized Merino wool throughout their product lines, with the goal of producing the most responsibly made product.