So I'm a bit confused here. My understanding of urethane foams (e.g. closed cell spray foam or polyiso) is that the blowing agent gases trapped within the closed cell structure slowly leak out over time and is replaced with air, depreciating the R-value. But then I see that certain companies advertise that there polyurethane sprayfoam products/kits do not off-gas. Is the leakage of the blowing agent not off-gassing, or is the manufacturer making a false claim? I'm assuming that they use an HFC blowing agent. Maybe I'm just missing something.