I wear a 7 1/2 - 7 5/8 pro fit hat and the XL is the correct size for me. I lucked out, because the Tayleins design goes with my bike and it fits my personality. Everything looks top of the line. The fabric is soft, and my ears have room to breathe. I haven't tested it on a hot day, but the vents appear to be engineered to help your head breathe. I'm stoked.