This baseball cap is made of cotton oilskin, like the McKinley. Waterproof oilskin caps in classic 6-panel construction, plain or fancied-up, have become favorites to wear before, during or after work. They are the perfect companions to all of our gear. S-21 5/8", M-22 1/8", L-22 1/2" - 23", XL-23 3/8" - 23 3/4" 1492