Gonex Cycling Bike Helmet for Adult Men Women Youth, Adjustable Road Bicycle Helmet(Black/White) Adult bike helmet with adjustable rotary internal regulator. Two sizes options aim to fitting different head sizes: M size is designed for teens and ladies with head circumferences of 55 - 58 cm. The L size is designed for adults' men and women with head circumferences of 58 - 61 cm. Premium Material: constructed with super lightweight, tough and durable PC, EPS foam material, shaping the helmet a sleek look and giving you a comfortable and no burden bicycle experience. Humanized Structure: The reinforcing skeleton holds the helmet together even there is a strong impact. It is also designed with detachable brim and washable inside liner, which is more convenient to use and clean. Excellent Ventilation: Helmet is designed with 33 Air Vents ensuring optimal air flow and minimal resistance, allowing air to pass through in efficient and easy way. Our helmet is CPSC certified.