Boot Docs Power Fit 70 Sock offers compression with merino wool for additional warmth and ideal support. The Power Fit Index (PFI) indicates how strong the overall level of gradual compression is: PFI 50 designates light compression, while PFI 90 is classified as strong and is therefore only found in our performance series. The special technology used for Boot Doc Power Fit Socks enables them to provide evenly distributed pressure around the ankle with graduated compression from bottom to top. Boot Doc Power Fit socks gently support muscles and tendons during all levels of sports. This helps keep your legs and feet feeling refreshed after even a long day of skiing, running, hiking, etc. The Boot Doc Power Fit design provides stabilizing support for the whole foot. More performance, better support, and as a pleasant side effect, warmer feet that feel refreshed. Boot Doc Power Fit Socks with compression stand out from rivals because of their high-quality workmanship and maximum comfort.