What is half pound foam?

Half pound foam is an open cell polyurethane foam that uses only water as a blowing agent. The density is only ½ pound per cubic foot and it can be distinguished by open pockets of air throughout the foam. Open cell foam is permeable to water and is not rigid in composition. Actually, open cell foam feels soft and spongy to the touch. Open cell foam is less expensive than closed cell foam because less chemical is needed to achieve ½ pound density, and it has a much lower R-value. Half pound foam expands about 150 times its original volume to form a semi-rigid, non-structural plastic. This SPF typically has an R-value of approximately 3.5 per 25.4 mm (1 inch). Half pound foam must be covered as per building code requirements for the protection of foamed plastics from sources of ignition (spark, fire, etc.) Half pound foam manufacturers have not yet found an environmentally sound way to deal with all of the excess waste left over after installations. Half pound foam is not a vapour barrier.