Polyurethane insulation fires in homes

Exothermic polymerization of polyurethane sprayed too thickly (more than 2 inches) self-ignites. Demonstrated experimentally by Tom's group with cast blocks. Codes now restrict layer thickness.

Advantages?

Student: Fire.

Fire — thermal mass could be a very good one, although it turns out insulation is better. Stone and concrete actually have low thermal conductivity, much lower than metals, but nowhere near what air gives you when you have fiberglass insulation, which just traps a bunch of air. Or polyurethane is so good that it burns down homes. Have you ever heard about polyurethane burning down homes? It's an exothermic reaction — to form the polymer. We got it up to a couple hundred degrees. We just made blocks and cast the polyurethane and measured it. The codes say you're not allowed to put it down in layers more than two inches thick at a time. People go in spraying it in homes, and they would spray it four inches, six inches thick, and it's such a good insulator that the exothermic nature would basically ignite it. So you burn down your home by putting in insulation. Now they have codes and standards to correct for it.