The Bridgedale Summit sock is a superbly made sock with WoolFusion Technology where the tough natural fiber new wool is fused 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 narrow feet or to snug up the fit of your boots if they feel a little too loose. 41% New Wool, 34% Nylon, 18% Polypropylene, 1% Lycra