Your refrigerator example got me thinking about an idea I had for insulation the other day. Why not use popcorn? It has the same basic properties of polystyrene insulation. Biggest problem I can see with it is that if the bugs get to it, your fridge is dunzo. Turns out I'm not the only one to think of this. https://www.independent.co.uk/news/science/popcorn-home-insulation-gottingen-university-b1962592.html