The Darn Tough Over-The-Calf Cushion Sock features terry rib knit, for custom fit.High density cushioning on foot bottom and around lower leg. Custom shrink treated Merino wool. Ribbing above the ankle ensures a proper fit. Reinforced heel and toe. Elastic support around the arch. Ring toe construction for a comfortable, invisible seam. Specs: 68% Merino Wool, 28% Nylon, 4% Lycra® Spandex Sizing: Small: Wmns 4-6.5, Euro 35-37 Medium: Mns 6-8.5, Wmns 7-9.5, Euro 37.5-41 Large: Mns 9-11.5, Wmns 10-12.5, Euro 41.5-43 XLarge: Mns 12+, Euro 43.5+