The Alder Burn fin socks are made from 4mm thick soft double-lined neoprene with glued and blindstitched seams and a grippy hard wearing outsole. Designed to be worn under your fins for comfort and warmth. S fits size UK 6-7 M fits size UK7-8 L fits size UK 8-9 XL fits size UK 9-10 XXL fits size UK 11-12