I keep looking for a foam product that would:
1. Be strong enough that people wouldn't fall through it,
2. Have a surface I can glue to or paint on,
3. Be inexpensive (or at least comparable to other wall materials),
4. Or be some kind of laminated foam or even plastic.
I've even considered using Foam Art Board since it comes in 4' x 8' sheets. But it is way too light to be considered as a wall board. Even if the foam can't be real strong structurally I do have access to veneers and other materials to cover the foam to strengthen it.
I look forward to reading your ideas on my alternate interior wall structure problems. My key problems to building there are vermin, termites and high humidity in the lower regions of Central America. Termites are not a problem for structural materials as the local hard woods are like Lignum Vitae (Iron Wood) and the termites don't eat that.