Legendary performance, style and comfort. Giro's Atmos II utilizes their Thermoformed SL Roll Cage reinforcement, a breakthrough in helmet architecture that allows greater ventilation without compromising a helmet’s integrity. The compact shape offers matchless style, and features the sure feel of a Roc Loc 5 system that cradles your head comfortably and securely. It’s no wonder this helmet continues to be a favorite with road, XC and cyclocross riders worldwide. - Small = 51-55cm - Medium = 55-59cm - Large = 59-63cm