Yours is good info, fellows.

I googled a bit on the purpose of the styrofoam "absorber" (as it is
called on parts sites). I thought this was interesting (from
http://www.car-stuff.com/toyotabumperabsorber.htm):
"... it is the Toyota bumper absorber that is usually made of
Styrofoam or plastic that is positioned in between the bumper cover
and the reinforcement to help strengthen the capacity of the bumper to
absorb the impact created during collisions. In most cases, bumpers
alone could not sustain the impact created during collisions, which is
why a bumper assembly should be completed for maximum protection. If
until now your bumper assembly is still lacking a Toyota bumper
absorber, better equip your auto with one now or you probably would
regret later on that you haven't. Bumpers are able to bounce the force
back to the object that has collided with your auto instead of that
force directly hitting your vehicle."

A lot of helmet designs use styrofoam, for one, so the above seems
reasonable.

Seems there is a fair amount of chatter and dispute about whether the
metal bumpers of say the 60s were better insofar as cutting down on
damage to the vehicle. Maybe so but ISTM manufacturers also sought to
lighten cars to achieve better gas mileage. Tradeoffs and all.