What’s the difference between a polyurethane core door and a polystyrene core door? Fire rating? Insulation?
Polyurethane is generally a better insulator (higher R-value with less material). I don’t think there is much difference in the fire resistance of the two materials and the construction of the door itself would likely have more impact on fire rating that which insulation you chose. However, polyurethane manufacture produces HCFCs which harm the ozone layer while polystyrene manufacture does not. Those are the main differences that I am aware of. Hope this helps.