I also use the blue foam sheets as pictured that I get from my buddy who works at a paint and body shop that all of their new body panels come wrapped in. It is water proof, liquid wipe right off, it's padded about 1/2" thick, doesn't catch on fire when welding and is slippery. You can just slide in and out right under the car.
the blue foam usually covers Ford bumpers. the smooth side is only on one side. VW uses similar stuff to wrap bumpers but puts the smooth part on both sides of the foam. lately VW has been using a different cheaper grade of foam. they also have started to wrap bumpers in special paper with 5 layers instead of foam on some bumpers. so i don't have access to as much foam as i used to get.
the nice part of the foam is it also has insulating properties when laying on cold concrete.
this also makes excellent packing material when shipping.
in the past i used to use rigid Styrofoam they use to put on the outside of houses. this can get $$$ if you have to buy it.
