The thermal conductivity ageing of a polyurethane foam can be sig nificantly influenced by the presence of a diffusion barrier, i.e., a bitumen facer. Such a bitumen facer attached completely to the surface of a PUR slab is generally con sidered a tool to slow down the exchange of cell gas with the environment. A com parison of gas chromatographic measurements of the transversal gas concentration profiles across the slab with gas absorption measurements on the facer material itself revealed that the effect of gas exchange is more effectively influenced by a dense polyurethane film on top of the foam than by the bitumen facer.
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