EPP( Expanded Polypropylene) is an advanced protective system that's significantly lighter than the traditional foam inside most batters helmets. In fact. EPP is one of the lightest protective materials on the market. Yet, it doesn't sacrifice performance. Our EPP impact absorption liner is part of a three layer protection system in the helmets. It distributes the load and energy of impacts across the entirety of the helmet shell, effectively dissipating that energy away from the play The EPP impact absorption liner is uniquely formed and ventilated to maximize performance and air flow throughout the helmet.