Made of 70% Cotton, 20% Nylon and 10% spandex. Cotton and Nylon ensures comfort and wearability while spandex provides the stretch and allows these socks to fit just about any foot size. Machine wash and dry. As these are from the UK, the packages are marked in UK and Euro sizes. We've found that they are very stretchy and fit a wide range of sizes. The medium size fits children's shoe size 11 to women's shoe size 9. The large size is a little taller and fits women's shoe size 7 and above.