Harley-Davidson Men's Cotton Skull Ivy Cap. Not just for the meek, H-D ivy caps are a powerful style statement for the true rider. Willie G. Davidson loved and still wears the ivy cap. It might be said he alone popularized the style for Harley-Davidson. Made of 100% cotton, the caps are fitted, and available in Medium to X-Large. Willie G’s skull logo design is embroidered on the front of the cap. It’s distinctive, and timeless.