Gain a better understanding of some the materials and technologies protecting your head
As someone who’s rung his bell more than he’d like to, I have the dubious honor of speaking about helmet technology from a very involved point of view. As the most serious crash of mine landed me in the hospital with some severe head trauma, I’ve taken a keen interest in helmets and the technology at work inside them. Look at any helmet review though and while you’ll surely see copious references made to weight, retention systems and ventilation, any talk of safety is often distilled down into a blanket phrase involving a few acronyms, some marketing speak and such and such helmet’s surpassing of ‘industry standards.’
So, in an attempt to lay out some of the basic information surrounding helmet technology and construction, I’ve put together this primer on what we as cyclists trust our lives to each and every ride.
Different Materials, Different Approaches, Same Goal
EPS, or expanded polystyrene should be instantly recognizeable—it’s been at the center of helmet construction for decades. In fact, the first purpose-designed cycling helmet (the Bell Biker, introduced in 1975) to offer an alternative to the rudimentary padded leather ‘hair net’ designs utilized an EPS liner with a hard shell—a construction method still used to this day. While the technology behind the material has certainly advanced, and construction methods have definitely changed, EPS is still the main player in the cycling protection biz.
Comprised of closed-cell foam, EPS starts out as small beads comprised of styrene and an expanding agent. When the beads are heated with steam, the expanding agent begins to boil, the styrene softens and the beads expand. Allowed to stabilize for a period, the pre-expanded beads, which now have a closed cellular-foam structure, are packed in a mold made in the same shape as the finished helmet and again reheated with steam. The pre-foamed beads expand further, completely filling the mold and fusing together.
In earlier designs, a hard shell would then be applied to the styrene shape. Now, using in-mold technology, the shell and the EPS liner are molded together, allowing for much more aggressive shaping of the shell to accommodate much more intricate vent designs and helmet shapes. It also prevents the shell from separating from the foam liner, and offers better transferring of impact force to the foam insert.
The shell of the helmet has three primary functions. First, it prevents sharp object penetration. Second, it protects the energy absorbing foam from abrasion. Lastly, it spreads out the force of an impact over a greater area. Most shells are formed from polycarbonate, while some helmets utilize carbon fiber to help save weight.
The major variable in terms of the EPS liner construction however, is that of density. At its most basic level, the less dense the foam, the more it deforms on impact, while conversely, the more dense the foam, the less it deforms. Different construction methods rely on different foam densities in order to achieve the proper blend of puncture and impact protection.
In select Kali helmets, Cone-Head technology is used and is comprised of two different foam densities used in a very distinct configuration. Lower density foam is nearer the head, while higher density foam is placed beneath the shell, allowing for a crumple-zone effect that dissipates impact force. The interlocking cone-like extrusions create a transition between the two layers, that helps dissipate energy sideways as the cones compress, rather than in the direction of the impact, and into the brain.
Also, the fact that the head is continually pushing into progressively more higher-density foam allows the head to gradually slow down, resulting in lower g-forces to the brain.
Created by physicist and educator Don Morgan of Australia, it is the product of his role as part of a research team funded by the Australian Federal Office of Road Safety to investigate the safety of bicycle and motorcycle helmets.
Comprised of co-polymer extruded tubes thermally welded into sheet form, Koroyd represents a completely different method of helmet construction. The combination of Koroyd’s precise extrusion and unique thermal welding process leads to a structure with both extremely efficient and consistent energy absorption properties.
Upon impact, the cores crush in a controlled manner (adopting an accordion-like form), decelerating the energy from the impact and reducing the final trauma levels. Used in ski helmets for several seasons by helmet manufacturers, Smith and POC, among others, Smith’s Forefront mountain bike helmet is the first helmet to use the material in a cycling application.
MIPS, or the Multi-directional Impact Protection System is based on the premise that most real-life crashes involve the helmet hitting an object at an angle resulting in rotational force which can be especially hazardous to the brain. (Despite helmet testing standards being based on the realistically unlikely direct impact to the top of the helmet.)
Drawing its inspiration from the brain itself, MIPS allows a helmet to move independently from the head in a controlled manner, reducing the severity of the rotational forces. The brain operates the same way in the sense that a layer of cerebral fluid between the skull and the brain allows for a small level of low-friction movement. With MIPS, instead of cerebral fluid, the rotation is allowed via a cradle built into the helmet cavity.
Used in many ski helmets and in mountain bike helmets such as the POC Trabec Race MIPS, its use is quickly growing.
At the end of the day though, the safest helmet is the helmet you’re wearing, so be educated, be safe and strap up. And remember, EPS, the building block of nearly every helmet on the market dries out over time, becoming brittle and losing its ability to safely protect your noggin. For that reason it’s recommended you replace your helmet every three years.