Regardless of the design, colors and shapes, the bike helmet must protect the cyclist's skull in the event of a crash or fall. Although its use is not mandatory, there are certain disciplines that for safety reasons and to prevent serious injuries require the use of a helmet: we are referring to all gravity- type disciplines, such as downhill and dirt jumping . Therefore, given the importance of the purposes of use of the helmet, it is essential that it guarantees adequate shock absorption capacity, ensured by the CE certification: a certified bike helmet is a device that complies with the stringent European safety regulations and therefore guarantees reliability.