Dan:

Polyurethane is the most widely used spray foam insulation in building applications and is available in one of two densities:  Open-cell foam and closed cell foam.

Open cell foams are porous and not impermeable to vapour, air and may absorb water.

Closed cell foams are far denser, providing both an effective vapour barrier, higher insulation value (~R6/in), and will not absorb and retain water to any real degree.

You are correct that once spray foam has been applied to a surface - be it a wall cavity in your house or your van - it is difficult to remove.  It is for this reason my earlier post suggested using thin, mats of high-density polyurethane insulation (it’s available in rolls from several manufacturers).

> On 15-May-2018, at 18:32, Dan N <dn92610@GMAIL.COM> wrote:
> 
> hi Julianna,
> 
> I've consider expanding foam option but dropped it because it's in there it
> won't be easy to remove if you to do some repair later. Also expanding foam
> is not a good insulation material because it's vert porous.