Interesting observation. Some old comments about using the expanding urethane foam in spray is the degree of expansion that can take place and the potential for pressure being exerted on fragile objects. The notion at one time was that this phenomenon was present relative to the size of the fill. Suggested solution was to fill the void partially and allow it to cure and then add more to complete the fill. Of course the other point of discussion is that products can continue to expand for quite a while after mixing (spraying). The other obvious issues are those of material off-gassing, and the intitial rise in temperature that results from the chemical reaction that forms the foam. I would love to hear from an expert in this particular material.