RaceQuip SFI 3.3 rated socks are knit from a blend of aramid and FRC fabrics to achieve a comfortable fire-retardant garment. The properties of this unique fabric structure create a lightweight fabric that performs like Nomex yet is much more cost effective. The Fire-Retardant Cotton (FRC) component of the fabric promotes a soft and supple lightweight feel. Since it's hypoallergenic, it won't irritate your skin like some other materials tend to do. This proprietary fabric blend is also superior at wicking away moisture from the skin and dries quickly. All RaceQuip fire retardant base layer garments are machine washable and retain their shape well. Exceeds SFI 3.3 rating and available in sizes from 2X-Small to 2X-Large - remember that racing base layers are designed and built to fit snugly so go up one size if you want it more loose fitting.