Balega's UltraGlide No Show Running Socks are designed to be lightweight and feature strategic protective cushioning. Engineered with Balega's proprietary Drynamix moisture management fiber and combined with a unique friction-free yarn, these socks keep feet cool and dry while allowing airflow for maximum comfort, performance, and durability. Featuring an additional cushion pad across the metatarsal area for additional protection, the design helps prevent blisters by encompassing moisture, heat, and movement. The UltraGlide incorporates PFTE (a synthetic fluoropolymer of tetrafluoroethylene) into the fabric to act as a lubricant, which reduces friction and wear. This unique lubricant is also responsible for controlled heat management, reducing heat caused by static and kinetic function to keep the skin cool. UltraGlide socks feature a contoured left and right knit construction to ensure that each sock fits the foot properly. This unique design eliminates excess bunching at the toes and prevents the sock from sliding down into shoes during activity. Sizing: Small (US Men's 4.5 to 6.5, US Women's 6 to 8, European 36 to 39.5), Medium (US Men's 7 to 9, US Women's 8.5 to 10.5, European 40 to 42.5), Large (US Men's 9.5 to 11.5, US Women's 11 to 13, European 43 to 45.5), X-Large (US Men's 12 to 14, US Women's 13.5 to 15.5, European 46 to 48.5).