In the previous article I said I could use both sides of the advertising board as bed material. Well the back of the board is a thick layer of a leathery sort of plastic, I think it may be PVC. I can certainly deposit ABS onto it, but it sticks so well and is so tough I found it completely impossible to remove.
The front of the board has a very thin layer of plastic with paper behind. That may also be PVC, but being so much thinner is easy to peel away.
Interesting that ABS appears to bond so well to PVC, if that is what it is.