One Size Fits Most The Peter Grimm Radio Waves Lifeguard is hand woven into a Herringbone Weave and made from 100% Straw. The 4.5 inch brim and premium underbrim lining provide excellent UPF 50+ Sun Protection. An adjustable chin cord will keep your hat secure on a windy day. The elasta-fit comfort band allows enough stretch to fit most men and women.