Bern Berkeley Helmet with Knit Certified ASTM F2040, CPSC and EN1078 Zip Mold: Patent-pending liquid injected high impact foam fused to a tough polycarbonate shell. Entineered seamless, tapered and thinner. It's ultra-lightweight. Sink Fit, Lowest Profile - So your helmet fits around your head - not on top of it. Deep fit for maximum comfort and an ergonomic profile. Doesn't look like a spaceship landed on your head Fits Head circumference 54-55.5 cm or 21-21 7/8 inches