The Complete Handbook of Motorcycle Helmet Parts & Accessories

Chapter 1: Understanding Motorcycle Helmet Parts & Accessories

Open a modern motorcycle helmet and you will not find a single piece of safety equipment. You will find a system of several dozen interacting parts, each with a specific job that influences how the helmet performs in a crash, how it feels during an eight-hour day in the saddle, and how long it remains safe to use. A helmet is not an object that can be judged by poking its outer shell. It is a carefully calibrated assembly of separate components - some structural, some comfort-oriented, some electrical - that must work together. Understanding those parts and how they fail is the basis of every rational decision you will make as a buyer, an installer, a maintenance professional, or a seller.

The primary function of a helmet is energy management, not shock absorption alone. In a crash, your helmet must do two things simultaneously: distribute the initial impact force across a wide area, and then progressively crush a compressible layer to slow your head's deceleration to a survivable rate. The outer shell, typically made of polycarbonate, fiberglass composite, or carbon fiber, handles the first task. It resists penetration, spreads the load, and protects the inner layers from being punctured by sharp debris. But it is the inner liner, almost always an expanded polystyrene (EPS) foam, that does the serious damping work. The shell deforms slightly; the EPS crushes permanently. This crushing action converts kinetic energy into heat and deformation energy, reducing