Historically, both gaseous and liquid blowing agents have been used in rigid polyurethane insulating foams, depending on the requirements of the application and the manufacturer. Since the elimination of HCFC 22 and HCFC 141b as blowing agents for rigid polyurethane insulating foams in the U. S., HFC 134a and HFC 245fa have become the blowing agents of choice where insulation is critical and the use of flammable materials is not feasible. Insulating foams used in household refrigerators and freezers typically require the lowest thermal conductivities and therefore use the highest levels of blowing agent. However, in applications such as entry doors or refrigerated trailers that do not require such low thermal conductivities, lower levels of these HFC blowing agents can be used. Despite the widespread use and well known advantages of HFC blowing agents, they still have one major drawback - significant Global Warming Potentials (GWPs) relative to carbon dioxide or hydrocarbons. Over the past few years, a number of low-GWP alternatives to HFCs have been proposed by the major suppliers of halogenated chemicals [1-6]. Bayer MaterialScience has conducted a laboratory study that compares the performance of some of these liquid and gaseous low-GWP blowing agents to their HFC counterparts. In this paper the performance of a gaseous low-GWP blowing agent is compared to that of HFC 134a in polyurethane foams containing both high and low levels of blowing agent. Likewise, foams blown with both high and low levels of a liquid low-GWP blowing agent will be compared to the corresponding foams prepared using HFC 245fa.
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