Features of the Darn Tough Men's Willoughby Micro Crew Lightweight with Cushion Sock Performance Fit: No slipping, no bunching, and no blisters Fine Gauge Knitting: Unprecedented durability and our unique ?put it on, forget it?s on? feel Fast Action Wicking: Pulls moisture away from skin. Fast drying All Weather Performance: Cool in the summer, warm in the winter Guaranteed For Life: No strings. No conditions. For life Merino Wool is fast drying, breathable and odor resistant for all-day comfort Fabric Details 53% Nylon, 44% Merino Wool, 3% Spandex Lycra