My thoughts on the tatoo polypropylene helmet

James of Bicycle Design first brought the Tatoo folding helmet to my attention about a week ago.





Since then, the various popular geek blogs have picked up Fast Company's critique of the Tatoo helmet.

Firstly, one of the Tatoo innovations: It's made completely of polypropylene and is recyclable. Bicycle helmets are mostly made from expanded polystyrene with other plastics and glues that make recycling difficult.

And that leads to the problem with Tatoo: It's not made with crushable polystyrene foam. The Tatoo design website touts the high "absorption power" of expanded polystyrene as well as its lightweight. There's a reason helmet manufacturers overwhelmingly use polystyrene, though: you get a lot of protection for the weight. They're designed to crush on impact to protect your head. The bouncy property of polypro might make your head bounce as well, resulting in increased trauma on your brain.

I'm told that expanded polypro is used in some helmets, especially those that are designed for multiple hits like multisport helmets. You'll note that multisport helmets tend to be heavier and less well ventilated than the Tatoo bike helmet seems to be. I imagine there's a reason for that.

James (of Bicycle Design, again), points, however, to some criticisms of current helmet design: namely, there's generally little evidence of crushing in real accidents.

What in fact happens in a real crash impact is that the human head deforms elastically on impact. The standard impact attenuation test making use of a solid headform does not consider the effect of human head deformation with the result that all acceleration attenuation occurs in compression of the liner. Since the solid headform is more capable of crushing helmet padding, manufacturers have had to provide relatively stiff foam in the helmet so that it would pass the impact attenuation test.

Cozy Beehive has a pretty good "How Helmets Work" article if you want to look into this a little more deeply. I live just a few blocks from the world headquarters of Bell Sports / Giro / Easton, so I might take a stroll down there and ask for their input on this. Unfortunately, the person I know best at Bell is retiring from her job at the end of this week, so I guess I need to cultivate a new contact there.

B+ on creativity and effort, C- on researching actual requirements for bike helmets.

For a recyclable helmet designed with US CPSC helmet safety standards in mind, see Logan Vickery's Eco Lock bike helmet.