Darn Tough Women's Thermolight Over The Calf Ultra-light Socks are the synthetic version of their lightest women’s snowboard and ski sock (the Women's RFL OTC Ultra-Light Sock is the merino wool version of this sock). This sock is knit with Thermolite® Polyester, a unique insulating fiber engineered to provide warmth and wicking comfort, without weight. The Thermolite OTC Ultralight provides all of the fit and structure features of its wool counterpart, including the True Seamless™ toe construction for a smooth fit around the toes with no pressure points of chaffing in the form fitting toe box, a sculpted heel, and integrated arch support, making this one of the finest fitting performance sock on the market. These socks are designed for the snug fit of a modern ski boot, especially those that have been custom fit for a precise integration between the foot and the boot, and crafted for women who prefer to wear a synthetic sock over one containing wool. If you have issues with wool, this sock is your obvious choice. If you run hot, or are working particularly hard and don’t need the extra insulating value of a wool sock, this sock will provide you with the fit and integration into your boot you’re looking for.