Li ing the lid How British start-up Hexo brought 3D printing to cycle helmets
For someone with an unusually large head, finding cycling helmets that fit is a tough business. I don’t imagine I’m alone in experiencing this, and even if you’re fortunate enough to be in ownership of a well-proportioned noggin, the fact most helmet companies offer just three sizes – small, medium and large – means it’s unlikely anybody gets a helmet that truly fits.
My interest was piqued, then, at Hexo, a British start-up five years in the making who are in the business of custom-fitted, 3D-printed lids. They take a scan of your head to produce a unique helmet fitted to you. Hexo aren’t the first to attempt to use 3D printing in this way – Canadian Kickstarter project Kupol are doing the same thing – but Hexo are the first to add the custom element.
This customisation, from both a fit and safety perspective, is essential to their idea, but its design and materials are just as important. It’s made from Polyamide 11 (or Nylon 11), a bioplastic (a renewable material) which you might have seen elsewhere in the cycling industry, chiefly in the soles of shoes. It’s absorption, flexibility and burst strength make it a popular material in the automotive, aerospace and oil and gas industries, primarily in tubing.
And it’s Polyamide 11’s absorption and ductility (stretching under stress) properties that persuaded Hexo’s founders, after a year of testing different materials and 3D printing techniques, to settle on it. Using a honeycomb structure (hence Hexo), they say its 68% better at controlling impact than EPS foam, the polystyrene that’s dominated the helmet industry for decades. After impact mechanics tests, not only does it pass European safety standards (CE EN-1078), they say, but is safer than foam helmets.
Jamie Cook, Hexo’s founder, began work on Hexo at university, at both University College London where he studied mechanical engineering and the University of Oxford, where he’s spent the last three years working on Hexo, along with co-founders Henry Neilson and Georgie Smithwick. It all began at UCL, where Cook, an international-level rower and bike commuter, was challenged by his
professor to take a product from the everyday world and improve it.
“I deconstructed several bike helmets in the lab. I hadn’t ever thought about it much before but once I took it apart I was perplexed that a basic material such as polystyrene foam was still so widely used in cycling helmets.
“It was during my research that I found that every design method for energy absorption assumes that the contact area is constant - but that’s not the case for a curved surface. We needed to design a helmet for the head’s unique curvature. This foam was designed in the 1960s for flat packaging – and heads are not flat!”
After materials, Cook also needed to think about structure:
“Cellular structures have the highest crush strength to weight ratio. That’s a great mechanical property when you’re trying to make a bicycle helmet.
“We need to design for the head’s unique curvature. The only way to make a curved honeycomb structure without distorting the mechanical properties is by 3D printing.”
On impact, Cook says this structure buckles and bends, involving more Hexo cells. This spreads force and reduces its peak, when compared to foam, and with it your chance of a serious head injury.
As well as its absorption qualities, Hexo says Polyamide 11 conducts heat eight times better than foam (an insulating material), so will help to cool you down. The outer shell of the helmet, made by TotalSim, British Cycling’s aerodynamics partner at the 2008 and 2012 Olympic Games, is colour customisable.
To shape the helmet to a rider’s head, Hexo use their own app to take a scan (developed by a third party), which creates a 30,000-point 3D mesh in seconds. The helmet, said to weigh 250g for a medium (a Specialized Prevail is 201g), is then “printed from data that is accurate to within a hair’s breadth”. The fabric that sits between your head and the helmet is removable and washable.
The helmet doesn’t have the MIPS (Multi-directional Impact Protection System) so widely seen in modern foam lids, a slip-plane layer designed to reduce rotational forces on impact. But given the Hexo is fitted to your head, it’s argued that this extra layer is surplus to requirements anyway.
The British-made helmet is still at the orders stage, but they’ve had a good reaction to it so far, touring up and down the country at various trade shows and appearing on BBC News.
Hexo certainly talk an impressive game and though we’ve yet to get our hands (or head) on a helmet, we’ve already had our heads scanned and will be reviewing it in a future issue.
It’s available for pre-order now at £349, with the first production models being shipped in March. Fitting will be available at a Hexo event in London in January and couriers are available to scan throughout Greater London and at two TBC retail partner stores. Check out their website, www. hexohelmets.com for further information.
On impact, the honeycomb structure buckles and bends, involving more Hexo cells. This spreads force and reduces its peak