Feature 1Adjustable Design: This helmet has a 3 adjustable system, with up and down adjustment function, 360 degree adjustment knob, and adjustable side straps, which can adjust height and circumference to make the helmet suitable for different head sizes. Suggest a head circumference of 58 to 62cm/22.83 to 24.41in. 2Durable Material: The helmet made of PC shell and EPS foam helps absorb and reduce the pressure caused by external impact, and secures the head during collision. Users wearing helmets will feel safer and more comfortable. 3Tail Lights: The helmet has 3 lighting modes, stable, slow flashing, and fast flashing, allowing you to maintain lighting during nighttime cycling. It can warn cars and help passengers behind you clearly identify your direction, providing the highest possible visibility on the streets. 4Strong Breathability: This product adopts a special aerodynamic design and 16 breathable vents, effectively reducing air resisting strength and sweat. 5Ultra Lightweight: The helmet is lightweight and comes with a soft inner cushion, chin strap, and padding to ensure a more comfortable user experience. It can be charged via USB, bringing convenience to users' lives.Item Type: Smart bike helmetMaterial: PC shell, EPS foamWeight: 404.00g/14.25ozApplicable Head Circumference: 58 to 62cm/22.83 to 24.41inBattery Type: Lithium battery (shipped with built in battery)Battery Capacity: 400mAh Package List: 1 x Helmet1 x Accessory1 x Charging Wire