The Zensah Compression Sock is designed with ProGrade Compression Technology. Developed to provide optimal amount of compression for runners, triathletes, cyclists, and other athletes, these socks increase oxygen blood flow to energize your legs pre-workout, enhance athletic performance during workouts, and aid in recovery post-workout. Zensah compression socks are the only athletic compression socks to incorporate arch support as part of the sock - allowing your legs to last longer during marathons, races, or long rides. Zensah Compression Socks make use of graduated compression technology to provide muscle support for both your shins and calves. The graduated compression also increases circulation which allows for faster recovery. The socks may be worn on the plane and during other travel to reduce edema and prevent any swelling that may occur in the ankle from reduced circulation. Zensah compression socks are made with special Zensah Fabric, which is both anti-microbial and thermo-regulating. The compression socks keep your legs cool in hot weather and comfortable in cold weather. Machine washable. SIZING (Shoe Size) - Small: Men 6-8, Women 7.5-9; Medium: Men 8-9.5, Women 9-11; Large: Men 10-12.5, Women 11+; X-Large: Men 13-15.