My insulation theory, take a look.

Ductape wrote:
There are pourable expanding foams for marine flotation applications.

There are so many use for Polyurethane foam, I am not surprised, basically I could just buy gallons of this stuff instead of little pouches.
But it's always the same thing, two parts that you mix together.
There are different densities, the lower density is like those cans of "great stuff" very brittle to the touch, same thing with those "froth pak" that you can buy at Homedepot, that's why I had professionals using commercial stuff insulate the upper walls and ceiling of my campervan, because I wanted a much higher density, it's not as brittle and gives more stiffness and soundproofing to my campervan.
Also you have two types of polyurethane, open and closed cel, closed cel doesn't absorb water, that's what I have in my van.

http://www.uscomposites.com/foam.html