I guess it might have the ability to hold moist air, but it is never wet to the touch like bat insulation that goes soggy.
I agree that the SM product is easier to work with and I would use it on any retrofit.
This is another shot of the same Airstream motorhome. If you enlarge this shot you can see the insulation through the cutout above center of picture. It has a blue color to it and looks to be a SM product in this unit? You can see the boards of insulation if you look close.
So the SM product did not do much for this unit.
"Just a comment about bead-board insulation. I work in the EIFS industry (Exterior Insulation Finishing System) we work with both types of insulating board - styrofoam and Expanded Polystyrene (EPS) or white bead-board. The way that EPS board is manufactured, bonding the larger beads together, acutally makes it more susceptible to holding moisture than styrofoam which is Extruded Polystyrene and is stronger, denser and has a higher R value than bead board. But as you stated, the real problem is: once moisture gets inside the walls or ceilings it is very difficult to dry out.[/QUOTE]