21 - 22 1/2 * Meets Safety Certification ASTM F 2040, CPSC and EN 1153 * Bern?s exclusive Zipmold? foam is a liquid foam injection process that provides a better weight to strength ratio so Bern can provide customers a thinner helmet. * Fit system at back of the head customizes to the shape of the head, keeping it stable and comfortable. * Compatible Bike/Skate/Warm Weather liner available (sold separately)