EPS stands for expanded polystyrene, which is a crushable foam also known as Styrofoam or commonly called thermocol. It is used as a helmet inner lining with the outer shell (made of ABS, fibre-glass or carbon fiber) and is normally covered with a layer of fabric lining and padding. EPS is very light in weight and responsible for absorbing the impact. It is what protects you in the event of a crash or impact on the helmet.