I am a fan of cardboard: from my early years I made many things out of it since it was cheap, easy to get and easy to work with: no fancy glues or exotic tools are needed, I even managed some pretty spectacular results getting it to bend. See below.
Now someone has made a real bicycle helmet using cardboard cells to absorb impacts.
Here is the WIRED page. Some people can't quite believe that something resembling corrugated cardboard can be a good impact absorber. On the other hand, how come it is such a puzzle? Much of the world's delivery goods arrive in boxes made of corrugated cardboard , and for good reason.
The stuff the helmet is made from resembles the inside of modern doors: hexagonal cell sheet, an idea also used in aerospace although they make theirs from metal or modern composite.
I am impressed and pleased by the gent concerned, and to top it all off
the Kranium company are offering helmets shaped to your head, (they scan your cranium!) which
would be a great safety improvement. Not sure I can afford a custom helmet but at least the potential is there.
Kranium also make a pretty good electric bike too, seen here.