Arai helmets are handmade to the highest possible standard, and although after many years the outside shell can look as good as new, it’s the EPS polystyrene liner that loses its ability to absorb impact over time.
Arai recommend replacing your helmet 7 years after date of manufacture and 5 years after date of purchase to maintain the maximum levels of protection.
The EPS liner is effectively the shock absorber of your helmet, absorbing the force of an impact onto the shell. This is done by the cells in the poly styrene being expanded (EPS = Expanded Polystyrene) and filled with air to absorb impacts. Over time, even when not in use, these liners lose their air pockets incrementally, after 7 years, dropping the shock absorbing ability of the liner below Arai’s safety standards. This is why we declare the helmet due for replacement so it can properly protect you against impacts.