Today’s motorcycle helmets all share at least four components in common to provide safety: outer shell, inner crush foam lining, comfort lining, and a retention device/chinstrap.
The hard, thin outer shell of motorcycle helmets are made of different materials including polycarbonate plastics, fiberglass, carbon fiber, and Kevlar and the higher-end helmets use a blend of materials. Each of the materials has a different mix of strength, ability to absorb impact, weight, and cost.
The function of the helmet’s outer shell is to absorb and spread the impact throughout the helmet, help avoid pointed objects puncturing the skull, protect the integrity of the inner crush lining, avoid abrasions, and to slide against the surface the rider lands on to help avoid neck injuries.
Below the outer shell is the dense inner crush foam lining, which is usually made of EPS (expanded polystyrene). Its role is to cushion the head while absorbing and spreading the energy of an impact. The density varies based on the estimates used by the manufacturer of the probable ranges of the speed of impact that will occur and the thickness of the foam is selected for both safety and practical purposes.
The last two motorcycle helmet commonalities, the comfort lining and chinstrap, are often forgotten when discussing safety aspects of motorcycle helmets. The comfort linings are made from softer foam, cloth or other high-tech materials to keep a riders head dry and cool. The chinstraps are frequently made of nylon with varying d-rings, snaps, clips, or other fasteners.
The most important function they both serve, and the only way to maximize all of the benefits from the research, development, and the new-age materials motorcycle helmets are made of today, is for a motorcycle helmet to fit snug and to stay on a rider’s head.