23 1/4-24 3/8 * Meets Safety Certification ASTM F 2040, CPSC and EN 1181 * 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)