In evaluation of the water vapour coefficient, the time depending permeation depth and the immobilized water during the absorption by Rhepanol ORG (PIB with black fillers) at 70 C is presented. The immobilized water content may be explained due to absorption on filler surfaces or in micropores. A very small water vapour diffusion coefficient was found with Rheanol ORG. It is presumed that this is due to both a high content of fillers with high specific surfaces, lamellar graphite and the very small diffusion coefficient of the unfilled PIB polymer comparable with vulcanized IIR rubber. It is therefore expected that Rhepanol ORG should exhibit a longer practical service life in flue gas desulfurization scrubbers and pipe lines, prolonging the risk of blistering to the lining. The corresponding data were also evaluated in hydrochloric acid.