Image courtesy of Smith

Bike Helmet Anatomy

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Anatomy Descriptions


The vast majority of shells, or the first layer of a helmet, are made from polycarbonate— a robust material that can be easily shaped or molded to many forms. Athin polycarbonate layer is bonded to an EPS layer, usually using an in-mold construction technique, which allows the shell and EPS liner to be formed together, creating a low-profile helmet.

Expanded Polystyrene (EPS) Foam Liner

Expanded Polystyrene is a rigid and tough closed-cell foam, used as the helmet’s primary safety mechanism in the event of a crash. On impact, the dense foam deforms and transfers kinetic energy around your head instead of through it. This severely damages the foam and its ability to redirect energy, and consequently, almost all helmets are rated for a single impact use.

Additional Liners:


MIPS Brain Protection System separates the shell and liner with a low friction layer. When a helmet is subjected to an angled impact, the low friction layer allows the helmet to slide relative to the head, providing additional protection against the rotational motion. Multiple manufacturers have adopted MIPS as an added level of safety.


Koroyd construction utilizes thousands of extruded co-polymer tubes to create a structure that complements the EPS liner. Upon impact, the tubes collapse in a controlled manner to decelerate energy to your head. Koroyd is used exclusively in Smith helmets.

Comfort Liner

A comfort liner is usually comprised of thin padding and moisture-wicking fabric. As the touch point between the helmet and your head, this liner is strictly for comfort and fit.


Forward and rear-facing vents are used to move air through the helmet for cooling purposes. Depending on the model and purpose of the helmet, there will be more or less vents and in varying sizes.


A visor is fitted to the front of the helmet and provides additional sun protection for the user’s eyes. Visors are most often found on mountain bike helmets, and are adjustable or removable for user preference.

Retention or Fit Systems

Usually in the form of a small dial at the back of the helmet, a retention or fit system will allow the user to adjust the fit of the helmet to their head. The dial reels in web, usually made of plastic, that is fitted in between the EPS liner and comfort liner of the helmet.

Cheek Pads

Full face helmets and some enduro helmets with a removable chin bar will include cheek pads. These pads provide some shock protection, but more importantly a secure fit and added comfort.

Chin Strap

The chin strap is an essential part of every helmet. This adjustable strap should buckle snug under the rider’s chin. It shouldn’t ride tight against the skin, but it shouldn’t be too loose either. When properly adjusted, it could play a key part in keeping the helmet on the rider’s head during a crash.