The Flight Socks by Lifesystems provide graduated compression that improves circulation, relieving discomfort & helping to prevent circulatory problems such as Deep Vein Thrombosis (DVT). Your ankle has little muscle in it & requires more stimulus than your calf to speed up circulation. These knee length socks provide graduated compression to stimulate blood flow. Compression level 14-17 mm Hg (18.7-22.7h Pa). This is size Large which is the equivalent of UK shoe size 9-12. Please note that it is important that you purchase the correct size. Made of 85% Polyamide Tactel Nylon & 15% Lycra Elastane.