One quick thing I want to mention is that you stated that spray foam cannot shrink. Well unfortunately that is not exactly true. I am a HUGE advocate for spray foam (when applied properly) but certain factors including the temperatures of the materials/substrates and the quality of the foam mixture can cause closed-cell foams to shrink.

I have never personally seen open-cell foam shrink post-installation and never hear about it. Usually what will happen is either the surface that the installer is spraying onto is too hot/cold or the actual materials inside the rig are too hot/cold. The gas that gets trapped inside the small capsules inside the closed-cell foam needs to live at a certain temperature until cured and cannot range outside of said temps.

Thanks again for you great post and I will certainly come back for more as I am now following your latest on Twitter. Please feel free to visit my blog at Soy-based-spray-foam.com