Intution says there is something to this. Some mushrooms can have a very heavy foam like structure. http://news.yahoo.com/s/ap/20070625/ap_on_sc/mushroom_insulation Then again, I have daydreamed of filling my walls with rocks. Funny, I remember an old foreman telling me sometimes I am dumber than a box of rocks...sometimes he said dirt, but I never got the difference.
Dirt can be composed of either mineral or organic or a combination of both. Rocks would be mineral. Dirt could contain some minerals finely ground such as sand. It could also contain massive quantities of organics such as manure. I don't know what he was trying to tell you , Outhouse. :)
Interesting on the mushroom insulation. Wonder how it will test out when it gets wet. :-?
The mushroom insulation looks interesting.
Rocks are smarter than dirt. Many people once kept pet rocks; know anyone with pet dirt? ::)