No one likes carrying a bulky bicycle helmet around. And as one designer after another tries to devise a way to make them collapse for storage, we're struck by how different everyone's approach is.
Julien Bergignat and Patrice Mouille's Tatoo Helmet is comprised of polypropylene strips lined with padded cells. Fastened at each end, the contraption rolls up like an armadillo. It's not terribly practical for carrying around, but assuming the connection points are strong enough, does seem it would withstand impact from the radial angles.
We Flotspotted/Trendletted Mike Rose's polypropylene Collapsible Helmet, which is considerably more elegant in terms of how it shrinks. The helmet compresses laterally, just about halving in size. However, while Rose has conducted drop tests for the helmet taking an impact from the top, we don't see any provision for providing the side-to-side structure you'd need for a lateral impact.
Inventor Jeff Woolf's successfully-crowdfunded Morpher helmet design also compresses laterally, and has won Popular Science's Safety Invention of the year for 2014/15. The helmet locks into the closed position via neodymium magnets. I'd like to see some explanation on the website as to how rigid this makes the helmet, but there is no technical description, just a statement that "Morpher has been designed to surpass all relevant safety standards."
The most recent design we've seen is Closca's Fuga helmet. Though they describe it as "folding," it doesn't fold at all, but rather telescopes down to roughly half-height. As with many of the other designs, there is no discussion on their website as to what provides rigidity from an impact along the axis it collapses along.
BioLogic's Pango folding helmet is made to fold in on itself from three angles. Because the folding design is hinge-based rather than compression-based, and when snapped together you have parts bracing each other in place, it seems it would be the most structurally sound:
It's subjective, but after looking at all of these, it seems the best solution to a folding helmet may not be a helmet at all.
We first spotted the Hövding "airbag for cyclists" a while ago, and it was first conceived of in 2005. By now the product's been around long enough that they've racked up both customer testimonials and praise from the insurance industry. And they really put their money where their mouth is, by showing crash-test footage and video demonstrations aplenty of the system deploying:
The only downside we can see is that there is a battery one must keep track of. But looking at the impressive protection statistics shown in the video, one does have to wonder if, compared to the Hövding, helmets really stand a chance.