The man at the body shop told me last week that (at least for the great majority, and maybe all cars) there's little or no metal in a bumper. He showed me on his computer the "exploded" view of the bumper system.

Instead, it's built to crunch, absorbing rather than transmitting the shock of a collision to the body. It's a "collision attentuation system", and as such it's built in about four layers or successive portions, each layer technically designed to collapse at a certain point, absorbing an exactly computed portion of the trauma.

The "metal" that you see is only an extremely thin plastic layer with a metal-looking coating.

Dave Oesterreich