SIZE: Elastic band on the backside, bike hats are suitable for all adults. Made of 100% premium polyester mesh fabric, more breathable, sweat-wicking and durable TWear it under helmet as a helmet liner, quick dry and breathable,Perfect to block sun and swear into your eyes UV Protection: The fabric is sun protection that protect you from sunburn The stylish design pattern allows you to look handsome even after taking off the helmet. Avoid the hassle of messy hair after taking off your cycling helmet. Fit Type : Regular