DURABLE - Built for both comfort and impact resistance with REINFORCED ABS SHELL & THICKENED SHOCK-ABSORBING EPS CORE.EXTRA REMOVABLE LINING - Skateboard helmet with two removable liner for different head sizes and easy to wash the sweat away.A HELMET for MULTI-SPORT - Smooth Ventilation System helps to protect and enjoy SKATING, CYCLING, BMX, MTB and etc.DOUBLE ADJUSTMENT - Well-attached & long-lasting adjustment dial and skin-friendly adjustable chin strap maxmize the best fit and comfortable wearing.HOW TO MEASURE A PROPER HELMET? - To find the right size bike helmet, start by measuring your head circumference, wrap a flexible tape measure around the largest portion of your head—about one inch above your eyebrows. Or, wrap a string around your head, then measure the length of string with a yardstick. Size Large is recommended if your size is between 21.3-22.8inch (54cm-58cm).