SFI 3.3 certified and priced for the weekend racer. OMP OS 40 Socks are breathable and comfortable for those long weekend days. These socks provide a dramatic increase in protection when worn with a driver's suit. Flame resistant underwear and socks are required by many race sanctioning bodies. These OMP OS 40 Socks is made of a very comfortable soft knit Nomex®. This is not the rough "waffle weave" fabric! SFI 3.3 Rated.