EIN Cycling Mountain Bike Racing Yellow Helmet Unisex Adult Women Safety Carbon Helmet Crash worthiness, not brittle to withstand the high intensity, strong foam density. Ultra-light, wind tunnel, duct design, effectively reduces wind resistance. High-quality foam layer, the adjustment within the twist, you can adjust the size of head circumference. Suitable for people with head circumference 56-62cm and the head-width below 21cm.