Urethanesimon

Hi I'm not sure if this is the right place, but... I am a the editor of Urethanes Technology International and UTECH-polyurethane.com and i would dearly like to know why we use some gases as blowing agents in rigid polyurethane formulations. I understand that they help to make bubbles of the right shape and size. My question is why are materials such as CFCs, HCFCs and now HFOs insulating gases? I guess there could be big dipoles within a smallish fluorinated molecule, but how would that make the gases insulating? Is there some kind of inter molecular attraction in the gas? Any help would be appreciated. Best wishes Simon