Foam Aquascaping?

[Cap'n]

I work with the nasty stuff every day, always while wearing a respirator. No way I would put expanding foam in my tank. Off-gasses for days, breaks down when exposed to sunlight, tiny abrasive particles.... I suggest reading an MSDS before using it.

I would, however, build a background out of foam, coat it with epoxy, resin, etc., then REMOVE the foam before placing in water. Good place to hide equipment as well.