Made with recycled polyester, breathable cotton, nylon, and spandex. S/M fits women's shoe size 5 - 9 and men's shoe size 4 - 8. X/XL fits women's shoe 9 - 13 and men's shoe 8 - 12. 1% of the sale of Blue Q socks supports the humanitarian work of Doctors Without Borders/Medecins Sans Frontieres.