Designed for adults interested in riding a bike. Sizes M: 54 - 58L: 58-62 Safety BSI certified: Complies with standard EN 1078 for bikes, inline skates and skateboards. 21 openings provide excellent ventilation. The 3D dial adjustment provides great comfort and a secure snug fit. Ventilation 21 vents Lightweight 290 g in size M. Ease of use 3D dial-fit adjustment for height and circumference. Designed for adults interested in riding a bike.