I looked at the foam insulation last night. It looks like there are 2 types available. One is blue but appears to crush easily and stay deformed (damage from handling evident and finger marks are permanent). The other is white with a silver backing on one side. That material is pretty squishy but appears to rebound when squished. I can't tell what a heavy liad would do, but I assume 1" foam would not be a 1" spacer.
Has anyone used a structural foam of any kind? I see a number of options online but have not seen anything in person yet.