Most helmets today have liners made of EPS (Expanded Polystyrene), a great shock absorbing material, but it will be permanently compressed when absorbing an impact, even a minor one. Using multi-impact EPP (Expanded Polypropylene) as core material creates a helmet that will protect your head over and over again. To date, both traditional hard shell and in-mold helmets have relied on Expanded Polystyrene (EPS) for shock absorption. EPS absorbs energy by plastic deformation on impact and results in permanent deformation. As a consequence, a helmet liner made of EPS will not be as good absorbing repetitive impacts. It would be a trend that most bike helmets will use a liner of Expanded Polypropylene (EPP) instead of the traditional EPS. The difference between the materials is that EPP does not deform permanently, which means it’s suitable for absorbing repetitive impacts.
