Bern Unlimited Diablo EPS Summer Helmet 21 1/2 - 22.5 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 Meets Safety Certification ASTM F 2040, CPSC and EN 1078 and WINTER UPGRADE KIT AVAILABLE SEPARATELY