Giro Adult Universal Fit Trinity Black White Skate Safety One Size, 21.25-24 in In-Mold construction reinforces the area around the vents and ribs, creating a one-piece exoskeleton, which allows the helmet to be lighter, more durable and better ventilated than traditional designs EPS liner and polycarbonate shell add reinforcement in crucial areas 22 vents provide excellent cooling and airflow Reflective back decal adds visibility Acu Dial retention system combines single-handed adjustment with a full fit band