: While it is unlikely that any of the foams would ever absorb so much water
: that they would sink, nonetheless, they do absorb some. So does wood for
: that matter. The amounts are so small that very precise scales would be
: required.

: Worse than absorption, though, is that the texture of the foam material tends
: to trap small quantities of water (droplet size)right on the surface.
: There is just enough water trapped to feed those pesky mildew spores, and
: to promote rot in unprotected wood. The trick is to leave enough room
: around the foam for air to circulate. That way the foam can completely dry
: out.

Paul, my thoughts have been to put the blue foam in while the hull and deck after they have already been fiberglassed inside. To put the layers of foam together and shaped to fit the hull and deck bow and stern while its easy to get to in both halves and then glass the halves with tape together. Any mildew spores would only be against glass and wouldn't effect the wood. If you think it would still be necessary for some ventilation, perhaps a small line of expanding gorilla glue could be put on the shaped foam and gently set into place leaving ventilation channles between the boat and foam. Thinking out loud.

John