All bike helmets seem to be made of a styrofoam-like inner material and a thin plastic outer shell with lots of holes for ventilation. I understand that helmets with more holes are supposed to be made of better foam to make up for having less material. Are there helmets that are made of stronger material that have fewer holes in order to provide more impact protection? or, are all bike helmets designed to have the same ANSI required impact protection with only a little extra strength for manufacturing variance? I would not mind wearing a little extra weight for a little more impact protection.