Our one-piece multi-density expanded polystyrene (EPS) liners are made by hand, not machines. We developed these complex liners so we can fine tune impact energy absorption in all areas of the helmet as needed, while keeping the size as compact as possible with uniform thickness. Depending upon the location of an impact, the area that absorbs the impact energy can be very small. For example, the top, sides and back are relatively large areas with ample surface area to disperse energy, whereas the forehead just above the eye port is quite narrow by comparison. That’s why our one-piece EPS liner integrates different densities according to the volume and position of each area of the helmet for maximum protection. This liner technology developed by Arai enables us to create a compact shell structure that’s both strong and light. There are 10 EPS densities to choose from, and depending on size there can be up to 4 densities in one shell. With up to 5 shells to cover all sizes of a model the possible combinations add complexity to our manufacturing process, but result in gains in protection.
In an impact, the human head contacts the EPS liner first, so we strive to use the softest densities whenever possible. We are able to do this because of our strong outer shell. Some manufacturers use a harder EPS liner to compensate for a weaker shell. A harder or thicker EPS liner can save cost and/or weight, thus altering the balance of protection between shell and EPS liner in order to pass a given standardized test. Designing specifically to pass a test, however, may not represent all possible impact scenarios. Arai believes that shells should be stronger and EPS liners should be softer in order to maximize protection for the rider.
We use various EPS densities to meet the specific performance criteria of each area of the helmet to achieve the impact-absorbing characteristic we want. EPS liners are designed specifically for each size helmet to achieve Arai’s high performance goals.