Recently I came into contact with a material I had never used before - Celotex. In its "real" application, Celotex is used much the same as "pink foam", as insulation sheathing. Instead of being petroleum based, it's made out of natural plant fibers. In consistency, its essentially loosely packed particle board. In our application, we used it as a sound deadening middle layer between 1/4" Meso and 3/4" ply. Just wondering if anyone else uses this product as it wasn't something I was previously aware of.