Scholl Flight Socks are clinicially proven to help prevent Deep Vein Thrombosis (DVT) during long periods of inactivity, such as travel. Deep Vein Thrombosis is a type of blood clot that is more likely to occur when we are inactive for long periods, in cramped conditions and is exacerabetd by dehydration.Wearing flight socks can also help prevent swollen ankles and tired aching legs. Graduated compression helps improve circulation in the foot, ankle and lower leg areas. Compression factor 14-17mmHg Medical device Advanced hoisery technology Cotton feel with a comfort top Antimicrobial protection to help keep feet fresh Suitable from the age of 12 years old Look like normal socks SIZE GUIDESmall Shoe Size: 3-6 / 36-40 Calf Circumfence: 35.5-40.5cm Ankle Circumfrence: 22.5-26.5cm Foot Length: 23-25cm Medium Shoe Size: 6-9 / 40-44 Calf Circumfence: 38-43.5cm Ankle Circumfrence: 24.5-29cm Foot Length: 25.5-27.5cm Large Shoe Size: 9-12 / 44-47 Calf Circumfence: 40.5-45.5cm Ankle Circumfrence: 26.5-31cm Foot Length: 26.5-30.5cm