About this item CONSTRUCTION - ABS Hard Plastic Shell with EPS Liner. COMFORTABLE AND COOL - Classic skate style meets new-school technology. In the dirt or out on the street, this helmet is comfortable and cool. ACTION FIT - Designed for street and skate helmets, this streamlined fit system offers an adjustable, secure fit with the turn of a dial. SPECIFICATIONS - Small (51-55 cm), Medium (55-59 cm), and Large (59-61.5 cm) Sizes. Important: always take a head measurement. Head sizes and shapes can vary, even within an age range. Using a helmet that does not fit can be dangerous; 10 Vents.