Impact-Proof & Protective Material: The helmet is designed for multi-sport head protection with CPCS certified. The material uses a strong ABS shell and high-quality EPS foam to help absorb the impact and protect the head during impact. Adjustable & Multiple Sizes: Roller skating helmets are suitable for kids ages 4-12 years old, teens, adults. With an adjustable spin dial inside, you can flexibly tighten/loosen the helmet for a comfortable wearing experience. Three sizes for chosen: small 18.89"-22.04" (48cm - 56cm); Medium 20.47 "-22.83"(52 cm - 58 cm); Large 22.04'' -24.01''(56 cm - 61cm). Ventilated & Cool Helmet: With 11 ventilation holes, it conforms to the special aerodynamic design to reduce sweating and keep cool, while also reducing the high temperature caused by intense physical exercise. Comfortable & Safe Design: The thickened sponge is soft and comfortable, which can reduce the pressure on the head. It is detachable and easy to wash. We also include a set of linings to replace the linings.