Positron annihilation lifetime and Doppler broadening of annihilation radiation techniques were employed to investigate the relationship between free-volume hole properties and miscibility of ethylene propylene diene monomer (EPDM)/acrylonitrile butadiene rubber (NBR) blends. It has been found that there were positive and negative deviations in free-volume hole size (tau(3)) and concentration (I-3) as well as S-parameter from linear relationship of initial polymers indicating the immiscibility of the blend. The broadening in free-volume hole distribution by increasing NBR content in EPDM/NBR blend confirm the results obtained by finite term analysis. From the filling effect Of silica on free-volume properties of EPDM/NBR (75/25) blend, it has been found that the addition of silica up to 50 phr is the most promising concentration for electrical application. Furthermore, correlations were established between free-volume hole size and fraction combined with the results of electrical (dielectric constant and dielectric loss) and mechanical (stress at yield and strain at yield) properties. (C) 2008 Wiley Periodicals, Inc.