My background in in the building trades..........nearly twenty years now. I live in a bus; have for the past 12 years. I have tried various forms of insulation in my bus. Bubble pack; foam,,,.high denisty, and the softer blue foam; blown-in loose fill { it just vibrates down to the lowest possible level. Toally useless. } even tried the stiff yellow foam with the paper/foil backing.....[piss-ants love this stuff!!!!!!!] tore all the others out, and chose the fiber-glass. It simply works. Just like in my profession as a carpenter, its experience that teaches. The fiber-glass just holds heat. Foam, in my opinon, is not as efficient at retaining heat. And, if used, MUST be applied in a strict application...........i.e, there can be NO voids between each sheet; for air travel............air will travel around the foam......so you have to put calking between each seam........... It is just a space filler. On the other hand sure, fiberglass is toxic; but its the warmth we are seeking. These days, there is a more natural product available. Real nice value; good quality. Briefly stated, a Company shreds blue-denim, and preares it just like for fiber glass instalation. Its pricy, but, in the Trades, I am using it more and more. Just an option.