Styrofoam helmets. That made me laugh.

I'm not talking theory but facts. Metal helmets increased head injuries substantially, and reduced bullet and shrapnel to-the-head fatalities substantially.

Also, you've evidently never seen a real metal helmet, which has plenty of damping. http://en.wikipedia.org/wiki/M1_Helmet

The M1's predecessor, the Brodie also had a padded lining: http://www.amazon.com/gp/product/images/B0036C0MXY/ref=dp_ot...