The Trekker is our best selling sock and for good reason. The WoolFusion Technology blends tough new wool together with high performance Endurofil Polypropylene for excellent durability, moisture wicking, and insulation, This construction ensures dry, warm, and comfortable feet- mile after mile. Bridgedale so confident in the comfort and performance of this sock, they offer a 3 year guarantee of comfort satisfaction! We recommend this sock for medium width feet. 41% New Wool,37% Nylon,21% Polypropylene