Ultra light weight durable aerodynamic thermoplastic alloy shell; Helmet comes with motorcycle Bluetooth headset as bundle (installation required); 3 people intercom: Bluetooth 3.0 connectivity ranged in 800 meters; listen to and share music from phone, pad and phone calls with speed dialing; Advanced Waterproof, Dustproof and Sun Protection Design with FM Rideo; Large Battery Volume Ensures up to 120 hours Standby Time & Usable when Charging; 2 hours full charged; 8-10 hours intercom time; Removable and Washable Padding; Aerodynamic rear venturi-effect exhaust spoiler; DOT Approved; Meets Federal Motor Vehicle Safety Standard 218 (FMVSS 218); Helmet Size Chart

S 53-54 CM 20.9/21.3 Inch
M 55-56 CM 21.7/22.0 Inch
L 57-58 CM 22.4/22.8 Inch
XL 59-60 CM 23.2/23.4 Inch
Helmet Size Tips

(1)Wrap a measuring tape around your head about a half-inch above eyebrows
(2)Take measurement two to three times to pick the largest one.