Adjustable Bike Helmet:This bicycle helmet is designed for adults or youth,teen; suggested head circumference:52.5-55.5cm(20.7-21.9 inches).To determine the correct helmet size,please wrap a measuring tape around youe head,the tape should rest 1.5cm bove your ears and remain level around the circumference of your head.Front and Rear Led Light: Our cycling helmet is designed with USB rechargeable front and back light .While the front lights provide lighting, the rear lights provide higher visibility for the vehicles or people behind you, providing better protection on the city streets at night.The rear lights have 4 modes: constant, flash, slow flash, warning flash.You dont need to remove the helmet to change the light.Adjustable Size Function:Our road bike helmet for men and women with Dual Fit adjustable design,size adjustable dial at the back of the helmet and side straps helps to fit different head circumference.Turn the dial to adapt the built-in helmet framework for a perfect fit.High-quality Cycling Helmet:The bike helmet with lights has passed CE and CPSC certification. The one-piece structure combines EPS foam and high-density PC shells to ensure better shock absorption and provide safer protection. The bike helmet adult is protective and ideal for urban commuting, cycling,scooter riding, skateboarding; also suitable for city, road, electric, trek bike and etcVentilation: This adult bicycle helmets has 14 vents with inside air-channels to keep you cool and comfortable for a casual ride or a long day on your bike. The removable padding can be washed and provides optimal cushion for a long ride.