Reading back through my reply, I can see where I might have sounded offended, but I was not. So perhaps poor inflection-translation-through-typing on my part.
It seems as if there are two primary reasons to use foam to build:
1) less expensive than wood
2) lighter than wood
Is this a correct assumption? If so, hitting both is best, but if you could only hit one (expense), while gaining rigidity (for those who value structural rigidity over weight), it seems like it might be a decent trade-off.
One thing I do note in going through the installation instructions on the Home Depot page, it appears that it is rated for both internal and external construction use.
Also, regarding Prop 65 (again from Home Depot):
Proposition 65 notice for wood products is as follows: WARNING: Drilling, sawing, sanding or machining wood products generates wood dust, a substance known to the State of California to cause cancer. Use a respirator or other safeguards to avoid inhaling wood dust.
So wood itself carries the Prop 65 warning label. I guess nothing is safe... oh well, something's got to kill me
