Sensing element made of polyisoprene and nanostructured carbon black particles (mean size: 30nm, specific surface: 950m2/g) for organic solvent vapour (osv) detection have been produced. To create very sensitive and reusable sensor material for the air quality monitoring, we have to analyze possible sensor material osv detection performance. Using in-situ measuring technique we determined absorbed analyte amount by the composite, analyte induced elongation of the sample and electric resistance change(see Fig. 1). Mass-sorption data is the source for evaluation of sensor material suitability for vapour detection. First, we can calculate analyte diffusion coefficient in to the composite. Second, we can find out diffusion behaviour. From diffusion theory: , where Mt is mass uptake in time t, M∞ is mass uptake, when time (t) approaches infinity. n and k are constants. If n=0,5 then the rate of diffusion is much slower than molecular chain relaxation (Fickian diffusion). When diffusion is very rapid compared with molecular chain relaxation process, then it is called Supercase II and n≥1.The third one is non-Fickian diffusion (0,5<n<1) that occurs when the diffusion rate and molecular chain relaxation are comparable [1]. For sensor material with immediate response to vapour the value of n should be within 0,5≤n<1. Length and electric resistance measurements let us evaluate resistance change mechanism. We have found out that at short exposure time electric resistance of the composite increases due to tunnelling current decrease in thin layers of matrix between carbon black aggregates (see Fig.2. 1.tunneling). But further exposure of composite to vapour leads to extreme increase of R/R0 and it is related to destruction of the conducting network (at deformations larger than 0,018). The process can be described by equation (see Fig.2.): , where R is samples electric resistance, R0–samples initial electric resistance and Δl/l0–relative elongation of the sample [2].