What’s in a crash helmet: the components protecting your head featured image
Advice & Guides

What’s in a crash helmet: the components protecting your head

13 Jan 2019
Updated: 4 Feb 2022 Ever wondered what all the parts that make up a crash helmet are? Wonder no more...

It’s 65 years since the formation of Bell Helmets, who revolutionised head protection by introducing a polystyrene liner to absorb impact energy.

Helmets have changed in that time, but the essential ingredients remain very similar. We stripped this Shark Race-R Pro helmet down to its constituent parts to show what keeps your noggin safe while riding.

Outer shell

The bit everyone sees – usually painted and often covered in graphic decals – is the first line of defence in an impact. It disperses some energy by spreading it across its surface, or deforming, and stops objects from penetrating through the inner lining to the rider’s head.

Helmets like this Shark have shells made from resin-impregnated fibres - this Race-R Pro shell includes a composite of different fibres. Composite fibre shells like this are usually lighter than the cheaper alternative material - injection-moulded polycarbonate.

Polycarbonate shells are less costly to manufacture and tend to be more resistant to penetration by sharp objects; on the downside, they’re usually heavier.

Holes in the shell allow airflow and attachment of essentials like the fastening strap, visor mountings and covers for the vents.

Expanded Polystyrene liner

This is the helmet’s most active ingredient. The liner is made from expanded polystyrene (EPS), which compresses in an impact, reducing the deceleration forces experienced by the brain.

Different densities of polystyrene are best suited to varying impact speeds – greater density (a harder EPS) suits higher-speed impacts while a lesser one (softer) works better at lower impact speeds.

Many liners are multi-density, using the right density to suit the most likely impact speed at that part of the helmet. Once the EPS liner has been compressed it won’t re-expand, which is why helmets must be discarded after an impact.

Modern helmets have holes to allow air to come through from external vents and channels to help the air to circulate around the head. Press stud mountings are there to secure the foam comfort lining in place.

In recent years some companies have attempted to innovate with new materials for the impact protection liner, but the overwhelming majority of helmets still use polystyrene.


The third key ingredient is the strap that stops the helmet flying off your head. It’s two lengths of webbing riveted to the inside of the shell at the jaw, then secured under the rider’s neck using one of a variety of different methods.

The simplest securing method is the D-ring arrangement like the one used on the Shark in our photos. The loose end of the strap feeds through two D-shaped rings and wraps around one ring before being fed back through the other ring. Pulling this tight creates a secure and strong connection that is pulled tight every time.

The most common alternative is the micrometric buckle. With this style of fastener a toothed plastic section slides inside a buckle, which relies on the teeth to keep it fastened. Releasing a lever allows the toothed section to slide out and undo the strap.

D-rings, which can be fiddly, are favoured by racers, while tourers and commuters often prefer the convenience of the ‘quick-release’ micrometric system.

Most other methods of strap fastening have fallen by the wayside over the years, though ‘FidLock’ is an emerging new arrangement that uses a strong magnet to fasten the strap securely.

Comfort lining

The foam and fabric lining is purely there for comfort. It generally comprises two sections – a skullpad and cheekpads – that attach into the helmet and make sure it’s secured comfortably to your head.

The padding is often used to create different sizes, with thicker or thinner padding being fitted to the same size shell/EPS combination to make it suit a bigger or smaller head. The cheapest helmets will come in one shell size, with thin padding for the XL version and super-thick padding to make it fit an XS head.

For riders with smaller heads it’s worth seeking out a helmet that is manufactured in a wide range of shell sizes. This avoids wearing an un-necessarily bulky and heavy helmet that’s carrying an extra load of foam to make it fit.

Most modern liners can be removed from the helmet for washing, and posher lids now come with anti-bacterial material covering the foam to create a more pleasant environment for your head.


A clear plastic shield across the eyes protects them from flying debris and bugs. It’s attached to plates that allow it to pivot on the side of the helmet so it can be raised out of the way when not riding, or to allow in air to cool the head or help clear mist from the inner surface of the visor.

Many helmets now have a Pinlock insert attached to the inside to stop moisture from the rider’s breath forming as moisture on the inner surface. These use tension to secure between two small pins attached to the visor, creating an airtight pocket that won't mist up.

This Shark is a race helmet and lacks a common modern addition – the internal sun visor. This is a ‘half-visor’ that slides down to shield the rider’s eyes from the sun. Tinted outer visors that let through less than 50% of available light are illegal for use on the roads in Britain, so having a tinted visor that can be quickly lifted out of the way is a neat solution to that problem.

Base plates

These screw to small threaded inserts popped into the shell, and hold the visor pivot points to the helmet. With this Shark, the visor slots over the pivot point and then two clips rotate to secure it in place.

Visor seal

This rubber strip secures around the edge of the visor aperture so the visor can seal against it, stopping rain getting in, and keeping out nasty draughts without scratching the visor as it rotates over the front.

Base trim

A rubber edging seal around the trim gives the helmet shell a more stable platform on which to sit, and ensures any sharp edges are guarded.

Vent covers

Any rider who experienced the first full-face helmets in the 1970s will attest that holes to allow air into the helmet are an excellent innovation. Equally important are covers to block them up again. The smaller covers open to expose two holes on the top of the shell, while the larger one covers the larger hole by the rider’s mouth, which is designed to direct airflow to the visor to get rid of mist that forms on the inside surface of the visor.