You "know" ?
Can you prove it? Or you THINK it made a difference? Or do you LIKE to believe it?
I meant I "know" at least 5 persons that had bike accidents (involving cars or not) where the helmet did make a difference.
But if you get hit by a car, a cm of Styrofoam is not going to make much of a difference. And I say this as someone who wears a helmet mountain biking and takes it off on the bike lanes.
I know at least 5 cases where this cm of styrofoam *made* a difference between a light injury and a very severe one. The latest case did not involved a car at all. I guess you will find out you are wrong the hard way, although I do not wish that to you...
//GO.SYSIN DD *, DOODAH, DOODAH