Pyrrole was polymerized in the presence of anhydrous ferric chloride as oxidant and p-toluene sulfonic acid as dopant. Polypyrrole-coated short nylon fibers were prepared by polymerizing pyrrole in the presence of short nylon fibers. The resultant polypyrrole (PPy) and PPy-coated nylon fiber (F-PPy) were then used to prepare rubber composites based on acrylonitrile butadiene rubber (NBR). The cure pattern, direct current (DC) conductivity, mechanical properties, morphology, thermal degradation parameters, and microwave characteristics of the resulting composites were studied. PPy retarded the cure reaction while F-PPy accelerated the cure reaction. Compared to PPy, F-PPy was found to be more effective in enhancing the DC conductivity of NBR. The tensile strength and modulus values increased on adding PPy and F-PPy to NBR, suggesting a reinforcement effect. Incorporation of PPy and F-PPy improved the thermal stability of NBR. The absolute value of the dielectric permittivity, alternating current (AC) conductivity, and absorption coefficient of the conducting composites prepared were found to be much greater than the gum vulcanizate. PPy and F-PPy were found to decrease the dielectric heating coefficient and skin depth significantly. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012