CPom, I think you're missing the point. I do believe the original poster is worried that when hit, the bumper will transmit all the energy of the impact into the vehicle, and with no crumple zones, the occupants will get hit with all that energy and get whip lash or otherwise thrown about. Least ways, that's what my impression was.

Chris Enos (Chino, CA)

'91 Isuzu Amigo "Rover" (Camaro 3800 swap in progress / 2.25" exhaust)
....(SOA / Custom rear bumper / CB / HAM)