The saga of alternative blowing agents for polyurethane foam insulation seems never-ending, and new chapters are still being written. In both residential and commercial refrigeration applications, the blowing agent CFC-11 had been the standard for years until banned by the Montreal Protocol because of its ozone depletion potential (ODP). Given the challenges of quickly finding ideal alternatives, HCFCs such as HCFC-141b, with a somewhat lower ODP, were approved as a temporary alternative until better blowing agents could be found.