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by James Huang
September 30, 2016
Photography by James Huang
Expanded polystyrene (EPS) foam has been the predominant energy-absorbing material for bicycle helmets for decades. It’s light, comparatively easy to form, and seems to do a pretty good job of protecting our noggins when used correctly. In short, it works. But is that the best we can do? Koroyd believes its polymer honeycomb network can do better — and the story behind how it came to be has nothing to do with bicycles.
Koroyd is a truly bizarre material. At first glance, it appears as little more than a honeycomb-like network of polymer straws, with an unmistakably fluorescent green hue, that appears to have been made by a swarm of radioactive bees. While colorful, it’s not exactly something many would naturally regard to be an effective means of absorbing significant amounts of impact energy.
Nevertheless, the engineering principles behind the material are sound.
Koroyd is certainly unusual looking stuff, and the way it’s manufactured is utterly brilliant.
Expanded polystyrene and other energy-absorbing foams absorb impact energy through deformation. During a crash, the foam compresses and becomes more dense — essentially turning more into compacted polystyrene instead of expanded polystyrene — and the impact energy is dissipated as heat. While the material’s low cost makes it appealing to manufacturers for obvious reasons, it’s also highly formable and tunable through parameters such as density and cell size, which offers helmet makers design flexibility.
In contrast, Koroyd behaves more like a series of hollow columns, which collapse on themselves upon impact — much like stepping on an empty beer can. It’s through this engineered structural collapse that Koroyd absorbs and dissipates energy, similar to how automobile companies build crumple zones into cars and trucks to protect vehicle occupants. Like EPS, Koroyd’s energy absorption properties can also tuned, in this case by altering the tube diameters and material densities.
Inventor Peter Sajic was originally focused on using individual tubes as crush structures in aerospace applications. Koroyd is instead a network of polycarbonate tubes welded together, but the basic principle of how it absorbs energy is the same. This sample has already been impacted, with the crumpled area shown on the upper half, and the lower half still available to absorb more energy.
The folks behind Koroyd claim that its novel material is not just an alternative to EPS, but that it does a better job of protecting your head.
According to data the company has collected in-house, an instrumented headform records 25-35% lower maximum deceleration rates when wearing a helmet made with a Koroyd liner, as compared to a conventional one made with an EPS liner of the same thickness. Moreover, the Koroyd-equipped helmet supposedly reduces by 58% the recorded Head Injury Criterion value, or HIC — a metric widely used by the automotive industry to gauge the likelihood of traumatic brain injury based on both the maximum recorded deceleration as well as the duration of the deceleration event.
Koroyd’s energy absorption properties can be altered based on tube diameter and material density.
Koroyd believes so thoroughly in the benefits of its technology that it has embarked on a Helmet Safety Initiative campaign, aimed to update the aging helmet test standards used by the bicycle industry to better reflect recent studies into the types of injuries riders actually suffer in a crash.
Without doubt, Koroyd’s claimed energy absorption properties are very interesting, and a small — but growing — number of bicycle companies, such as Smith Optics and Endura, are already incorporating it into bicycle-focused protective gear.
Yet where did this unconventional material come from? As it turns out, Koroyd’s origins have far more to do with airplanes than bicycles.
Peter Sajic is a veteran aerospace engineer, specializing in composite materials such as carbon fiber and boron fibers. Plane crashes were far more common in the 1980s than they are today, and like many engineers at the time, Sajic was keenly interested in figuring out ways to make flying safer. Accident reconstruction research was demonstrating that many passengers were dying not from the impact of the crash itself, but because their seats were detaching from the cabin floor, leaving their occupants free to rattle about inside like eggs in a jar.
“A lot of these fatalities and injuries could have been avoided if there had been some energy-absorbing capabilities designed into the seats,” Sajic told CyclingTips. “So we were looking at efficient ways of absorbing energy in aircraft seats.”
Sajic focused on the idea of using a tubular structure to attach the seats to the floor, with the thought being that the tube would buckle upon impact in a controlled fashion, instead of breaking away completely. In essence, the tube would act as a crumple zone to absorb the energy — and hopefully, save some lives.
Koroyd’s energy absorption properties is reliant on its tubular substructure, which crushes and deforms predictably based on proven engineering principles that are often used in the automotive industry. Whereas the crush structures used in cars and trucks are made of metal, however, Koroyd is made of a network of lightweight polycarbonate tubes.
It also didn’t take long before Sajic began looking at other applications for his nascent technology.
“Energy absorption was now beginning to gain interest in the car industry, so I was thinking, if we could develop a material that incorporated a lot of these tubes, we’d have the most efficient material on the market for absorbing energy. The beauty of a tube is that it’s an engineering element. Engineers understand the properties of tubes, and you can engineer the performance of a tube quite accurately, whether it’s buckling or bending or whatever you want to do with it.”
Engineering a single tube to act as a sacrificial crash structure is one thing; laying out a network of them to form a more readily used sheet is another entirely — and it’s here where Koroyd is particularly ingenious, not in terms of what it does, but rather how it’s made.
Each straw in a Koroyd panel is extruded as a dual-layer polycarbonate tube with a wall thickness of just 0.09mm. The interior tube is slightly thicker and provides structure, while the outer layer is much thinner and melts at a slightly lower temperature. Those tubes are then bundled together, hot air is passed through the network, and that outer layer melts together to form a unified structure.
Creating the honeycomb in this fashion not only omits conventional adhesives and glues that can often serve as weak points, but also retains each straw’s tubular structure, which is so critical to the material’s energy absorption properties.
Koroyd is extruded as long tubes, and formed as giant blocks. From there, it can be sliced as needed depending on the application.
Even after Sajic had figured out how to make Koroyd in panels, though, he still knew he had a big problem on his hands.
“Basically what we were making were sheets of material. That’s fine, but what do you do with a sheet? You’ve got to convert it to something. Shapes are very important for the design and aesthetics.”
Enter John Lloyd.
Pre-formed sheets of Koroyd can also be thermoformed into more complex shapes that are more conducive to sporting applications like helmets and protective armor.
Lloyd was in charge of product development at his family’s business — a giant in the motorcycle helmet business with a million units in annual sales under brand names such as Nitro and G-Mac — and he was on the hunt for the next big thing in protection. Lloyd and Sajic were connected around 2007 through a mutual business acquaintance, and the former quickly began lab testing to gauge Koroyd’s potential. According to Lloyd, that potential, in terms of safety improvement, was massive.
The global economic downturn unfortunately scuttled Lloyd’s hopes of incorporating Koroyd into motorcycle helmets, but the development time invested still yielded the ability to form those flat sheets into shapes that were more conducive for use in helmets and other safety gear, and without adversely affecting Koroyd’s protective qualities. Since Lloyd was forced to hold off on introducing Koroyd into the motorcycle world, he turned to the cycling market instead.
Drew Chilson was Smith Optics’ long-time development director, and like Lloyd, he was searching for alternatives to traditional EPS materials.
“EPS is a fabulous impact material, but it’s really constraining,” he said. “I knew there were some materials or geometries out there that could absorb energy. This hunt for alternative materials started in 2009. I had read some blurb on the internet about a new impact material and went, ‘Oh, that’s kind of cool; that might work’ — and then I totally forgot about it. I went to the Interbike show and I’m walking down the hall, and here comes this Scottish guy and he’s waving at me. He’d already been to the Smith booth and talked to our product manager, and he goes, ‘You’re Drew! You’re interested in my material!’ I had told our helmet category manager, Lindsey Johnson, that I was interested in this material, and she knew that I was on the hunt for different materials to do the job. [John Lloyd] had the same idea at the same time. He looked at the Smith product line and what we had done in snow, and went, ‘OK, those guys are doing something different. I should approach them first.
“So he approached us first and I wasn’t in the booth, but then he saw me in the hall and he just about tackled me. It was hilarious.”
Fluorescent green is Koroyd’s signature color, but there’s no reason other colors can’t be used.
Chilson and Lloyd wasted little time in exploring the possibilities, and just as Lloyd was quickly won over by Koroyd’s energy absorption qualities, so was Chilson when he tested samples for himself.
“We went into testing of the material itself and it was literally 50% better than EPS,” said Chilson. “EPS was the best of the rest, by a long shot — much better than vinyl nitride foams, much better than EPP, much better than a lot of the open-cell foam prototypes that people had sent us. That was our first ‘aha moment.’
“From there, we did a snow helmet. We modified some existing snow helmet EPS tooling so that it would produce cavities that could accept thermoformed Koroyd panels. We built prototypes, we tested it, and it ended up 30-40% better in the zones where we put it. At that point, we were off to the races.”
After a successful introduction in the snowsports world, Smith Optics introduced the Forefront mountain bike helmet in 2013, which was followed soon afterward by the road-oriented Overtake.
Smith Optics has followed up on those initial efforts with the new road-oriented Route and its off-road cousin, the Rover. Instead of using full-Koroyd liners, both use smaller Koroyd inserts that are strategically placed in the areas that are most often hit in a crash, along with low-friction MIPS liners that are also claimed to reduce the incidence of brain injuries. The more limited Koroyd placement leaves room for traditional vents and internal channeling for improved airflow — poor ventilation was one of the most common complaints on the Overtake and Forefront — and it also reduces costs. Whereas a MIPS-equipped Overtake costs US$250, the comparable Route is US$180.
Smith Optics has followed up on its first two Koroyd-equipped helmets with two lower-priced options. The road-oriented Route uses smaller panels of Koroyd that are placed strategically where Smith says riders are most likely to hit their heads.
While Koroyd supposedly offers benefits in terms of impact energy dissipation, the radial orientation of the tubes isn’t exactly conducive to air flowing through the structure.
Whereas the Smith Optics Overtake road helmet is more futuristic in appearance, the newer Route model is more conventional – and definitely less polarizing.
One area where the new Smith Route does particularly well is airflow around the forehead. Deep gaps in this area help keep the browpad dry, and sweat from dripping into your eyes.
Vents are only one piece of the puzzle when it comes to promoting airflow through a helmet. Internal channeling is perhaps an even more important aspect, and the Route’s more conventional construction allows for much more channeling than the full-Koroyd liner on Smith’s higher-end Overtake model.
The low-friction MIPS liner is claimed to add another layer of brain protection on top of the Koroyd panels.
The flexible VaporFit retention system on the Smith Optics Route helmet is quite comfortable, adjustable for height, and definitely very easy to use.
Three months of regular use in a Route has convinced me that this approach also produces a better overall helmet than the Overtake or Forefront. Although Koroyd proponents might suggest that the lower Koroyd content might adversely affect safety, the Route presumably still offers better-than-typical protection but is far easier to live with on a day-to-day basis. After all, the safest helmet is the one that’s on your head, not left behind on a shelf in your garage because it was too hot that day.
Is the Route the best helmet I’ve ever used? I suppose that depends on your definition of “best”. Is it the safest? That’s impossible for me to say.
But that Koroyd and its partners — as well as other similarly motivated companies like MIPS and its supporters — are drawing more attention to the topic of rider safety instead of performance metrics like aerodynamics and weight can be seen as only a good thing.
No one likes a helmet that’s so hot, uncomfortable, and heavy that you don’t want to wear it. And while it’s certainly nice that we have options that are lightweight, aero, and packed with convenience features, those are not the metrics by which helmets should ultimately be judged.
Is Koroyd the answer? That depends on who (and what) you ask, and truth be told, the company’s Helmet Safety Initiative could certainly be seen by cynics as a veiled marketing attempt to get more helmet companies to license its technology. Nevertheless, it’s difficult to argue against Koroyd’s contention that bicycle helmet test standards should be as stringent as the ones used in the automotive industry in terms of limiting the occurrence of traumatic brain injuries.
Regardless of the means, the overall goal of improving rider safety is a truly admirable one, and kudos to Koroyd for drawing more attention to the topic.