SM3 Youth Jettson Helmet. Anatomically engineered and profiled specifically for youth and younger riders, the SM3 Youth Helmet is optimized for MX, enduro and off-road use, and features a whole raft of technologies and innovations taken from Alpinestars range of adult helmets to deliver the optimal blend of performance, protection and comfort. Key Features: This lightweight helmet features a thermo-injected shell incorporating a special polymer blend enhanced by varying degrees of thickness that is engineered to deliver the optimal combination of impact protection and light weight. Lightweight outer shell is constructed from a technologically advanced impact-resistant thermoplastic in three sizes (Youth Small, Youth Medium and Youth Large). The SM3 Youth weighs 1170 grams (DOT).