Bern Unlimited Macon EPS Summer Helmet with Visor 22 1/2 - 24 in Thinshell EPS foam with ABS outer shell gives a durable and long lasting, low profile fit Excellent ventilation combined with angular vents to keep sharp objects on the outside Crank Fit dial on back of helmet quickly secures or loosens the fit around your head, super easy to adjust - even on the fly Meets Safety Certification ASTM F 2040, CPSC and EN 1078 and WINTER UPGRADE KIT AVAILABLE SEPARATELY