Motorcycle helmets protect twice. Regardless of the material, the outer shell distributes a punctiform impact of force through high elastic deformation energy and is intended to prevent the penetration of pointed or edged objects. The actual cushioning is provided by the inner material between the outer shell and the lining. This is usually made from special EPS rigid foam materials from the Styrofoam family, which absorb impact energy but only once, since an impact leads to compression and thus permanent deformation of the material. This is why helmets have to be replaced after accidents or falls, even if they appear to be undamaged from the outside.
Two groups of materials are used to manufacture motorcycle helmets shells: thermoplastics and duroplastics. Thermoplastics such as acrylonitrile butadiene styrene (ABS), polycarbonate or polyamide can be easily shaped when heated. They are therefore suitable for the injection molding process because large quantities of helmets can be produced inexpensively with them. Duroplasts and composite materials (e.g. aramid fibers, glass fiber reinforced plastic, carbon, Dyneema), on the other hand, require a complex laminate process. Shells made of these materials are particularly hard and unbreakable, but more expensive.
As long-term material tests have shown, duroplastics ageless quickly. With good care, their lifespan lasts at least eight years. Helmets made of thermoplastics that do not have an additional layer of paint can become brittle earlier in the event of strong ultraviolet radiation and other influences (solvents, petrol). The experts urgently advise replacing such helmets after around five years due to the diminishing protective effect. However, this period is recommended for helmets of all types with heavy use, since the insulating material also gives way and the helmet then no longer fits optimally.
Anyone who rides with an open chin strap takes away the protective effect of their helmet because it can fly off their head. Flip-up helmets may only be used with the helmet closed, otherwise the airflow would have fatal consequences. Exceptions are helmets whose chin bar can be pushed completely behind the helmet – but only if they have an additional certification as a jet helmet.
Very important point is Motorcycle helmets should not be pasted or painted. Solvent contained in the adhesive or paint can affect the stability of the helmet shell. An exception are the stickers from the Institute for Two-wheeler Safety, which inform first responders about opening the helmet or the chin strap locking system in emergencies, they have a solvent-free special adhesive.