GDM Duke DK-120 full face motorcycle helmet is DOT FMVSS-218 certified. Its shell is constructed using an advanced lightweight composite poly-alloy. It features five points of ventilation with removable and washable liner and cheek pads. It also includes a double D-ring chin strap and comes with two visors in the box. Please refer to the following size guide to determine your correct size. To choose your correct helmet size, please measure the circumference of your head 1" above your eyebrows around your head and refer to the GDM Duke Helmets size guide below. Please note that the size guide is for reference only and cannot guarantee a perfect fit. SMALL: 21 5/8 – 22 IN 55-56 CM | MEDIUM: 22 ½ -- 22 7/8 IN 57-58 CM | LARGE: 23 1/4 -- 23 5/8 IN 59-60 CM | X-LARGE: 24 -- 24 3/8 IN 61-62 CM | 2X-LARGE: 24 3/4 -- 25 ¼ IN 63-64 CM