21 - 21 7/8-Inch * Hard Hats are designed for slower speed impacts - MULTI-IMPACT design and DOES NOT meet the Single Impact rating for CPSC, ASTM or EN 1078 ratings; THIS IS NOT A HELMET * Soft and comfortable BROCK foam is the only fully open cell construction that permits full breathability around your head * Unique Construction very comfortable for a wide range of conditions * Separate Winter liner can be purchased to convert to either cold weather bike riding, or for skiing/snowboarding