FIT: One size fits most cycling helmets. Easily adjust from 54cm to 61cm to fit sizes small, medium, and large (not designed for XXL/62cm/24. 5 inches and up.) COMFORTABLE: bike helmet is padded, lightweight and aerodynamic to slice through the headwind. BREATHABLE: 24 vents and contoured design with inside air-channels force ventilation through and around the bicycle helmet for a cool, comfortable ride. SAFE: Constructed with high-quality EPS encased by PVC for top-tier protection. All Retrospec bike helmets are tested at a CPSC and EN lab for safety.