The Regulator fits most head shapes & will protect your head with the injection molded ABS shell & EPS liner to absorb the impact of bigger hits. The Jet Diffusion vent system with internal venting system & rear exhaust vents keeps a nice airflow to ventilate your entire head evenly, while maintaining airflow through your goggles so you remain comfortable & keep your goggles fog free. No need to wear a hat underneath as the upgraded soft cupping detachable ear pads will keep you warm. Not only does the Regulator helmet give you protection but goggle shelf & clip assures you won't lose your goggles after a bad wipeout. Check out full list of Key Features & alternative products below Size Guide: Medium fits 55 -56cm (S/M Shell) Large fits 57-58cm (LRG Shell) X Large fits 59-60cm (XL Shell)