I think Grigg is correct. When the Prius backed into my right front bumper of my '51 AD, the bumper went into the fender and dented it. The bumper itself, other than scuffing the paint, was undamaged. Thus, I believe it is spring steel.

Kent

1937 Chevy 1/2 ton
1942 Chevy 1/2 ton
1947 Diamond T Model 509
1951 Chevy 1/2 ton
1950 Chevy COE Model 5700 ~ "Barney" ~ And more pix