Here’s an interesting video that was produced by NBC as part of their Science of Design series for the Olympics.
Let me just say that the image of how the foam compresses after an impact reinforces my commitment to replacing my helmet after every impact.
Of course, helmet fit is an important component of helmet safety. The best engineered helmet in the world won’t help (at least much) if it doesn’t fit properly.
The video didn’t embed properly, so here’s a link.
http://www.nbcolympics.com/video/2012/science-of-olympics-designing-safety-helmets.html