[corksil]

Typically there are two types of "foam" with various independent properties.

Closed cell foam does not absorb water because the tiny little air bubbles in the foam are sealed. Think 'bubble wrap.'

Open cell foam will absorb and hold water. Think 'sponge.'

There are various grades of foam; each with their own unique chemical properties. Polypropylene, polystyrene, polyethylene, HDPE (high-density-poly-ethylene), LDPE (low-density-poly-ethylene), polyurethane, PVC (poly-vinyl-choride/PVC) and a few other common ones.

The word "foam" is actually a misnomer because when people hear the word "foam" they typically think of a sponge or something that is squishy and absorbent.

"Foam" has a working definition of "a mass of tiny bubbles" -- and all plastics are a formulation of such, each with varying and independent properties. Most plastic compounds consist of an extruded base compound, which is "cured" into a finished product with the use of an accelerant or hardener. From a chemical standpoint this is the same method of action accomplished by jb weld or bondo, or any epoxy/polyester casting resin with a two-part mixture.

All of this is probably way more information than you wanted to read, but maybe it will be helpful if you have a project in the future and need to know about this stuff.