Granvela A005 Mtb/Road Bike Helmets Cycling Mountain Racing Bicycle Helmet, Men Women Adult Keep Safety, with 21 Vents Adjustable Ultralight Integrally-molded Lightweight integrally-molded EPS bicycle helmet 24 Integrated Flow Vents to Keep Rider Cool Easy-to-adjust Webbing Ensures a Comfortable Fit. Head circumference: about 56-64 cm / 22-25.2 in adjustable Adult Bike Helmet, Ultralight, Integrally-molded Helmet Rear exhaust ports for enhanced air flow