Since their discovery in the early 40's extruded polystyrene foams (XPS) have been produced with various organic and inorganic blowing agents, and are now widely used as thermal insulators in building and construction. Blowing agent regulations have forced foam suppliers to look for new polymer - blowing agent - additive combinations. These must deliver high performance insulation, but must not compromise on high mechanical strength, foam integrity, and moisture resistance. This paper focuses on the thermal resistance of XPS blown with zero-ODP blowing agent (hydrofluorocarbon HFC-134a) and with carbon dioxide. IR-blockers such as carbon black and graphite reduce the thermal conductivity of CO2 blown XPS between 1 and 3×10-3 W/m.K depending on the concentration of IR-attenuators. Properties of a new XPS product using CO2 with IR blockers are presented. This product is CE certified and fulfills the requirements of the European XPS product standard DIN EN 13164.

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Insulation performance of extruded polystyrene (XPS) foams expanded with various halogenated blowing agents including HFC-134a or HCFC-142b was measured over time. Residual blowing agents were measured after aging up to 26 years. The diffusive transport properties of the blowing agents can be determined through the mathematical calculation of the heat transfer in the gas phase component of the foam thermal conductivity. These values are used in a Dow model which allows an accurate prediction of the long-term thermal resistance of extruded polystyrene foams blown with a variety of blowing agents including CFC-12, HCFC-142b, HCFC-22, HFC-134a, HFC-152a, and CO2. Excellent agreement was obtained between measured and predicted thermal conductivity values with samples stored in laboratory conditions, as well as samples extracted from field conditions, such as cellar and upside-down roof applications. The results confirm the slow diffusion rate of CFC-12, HCFC-142b and HFC-134a through extruded polystyrene foam, and demonstrate that HFC-134a or HCFC-142b-blown extruded polystyrene (XPS) foams meet the requirement for applications requiring excellent long-term insulation performance. HCFC-22 and HFC-152a are fugitive blowing agents in XPS foams, and the thermal performance of foams made with these blowing agents reach the thermal performance of CO2-blown foams after a short aging period.

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The addition of opacifiers in foams considerably reduces the radiative thermal conductivity and consequently enhances the insulation performance of the foams. In this work two different methods were developed to calculate the spectral specific extinction coefficient of opacified extruded polystyrene (XPS) foam material. Cell morphology and thermal conductivity of two identical XPS-foams, one opacified with 3 wt% carbon black as opacifier and one without opacifier, were thoroughly characterized. The experimental results were in a good agreement with the theoretical results obtained from two different computing techniques. These methods allow a good prediction of the specific extinction coefficient of arbitrary opacified foam material.