The O'Neal Hyperlite IPX helmet features a lightweight fiberglass construction paired with multiple oversized vents for maximum airflow and cooling. A Dri-Lex padded inner liner features an antibacterial polygiene treatment, it's ultra-plush, removable, sweat absorbing and washable. It features emergency pull straps on the cheek pads for easy and quick removal. The O'Neal Fidlock magnetic buckle allows for easy, single-handed fastening and release to provide maximum security while riding. Size guide: X-Small: 20-1/2" - 21-1/8" Small: 21-1/4" - 22-1/8" Medium: 22-3/8" - 23-1/8" Large: 23-1/4" - 23-3/4" X-Large: 23-7/8" - 24-3/4"