Polypyrrole films containing different dopant ions were electrochemically synthesized and the interaction between polypyrrole and water was evaluated by means of sorption isotherm, cluster function and d.s.c. It was found that the water sorbed in the polypyrrole behaved as a non-freezing bound water which was rather isolated and prevented from clustering over the whole experimental range of the relative water vapour pressure from 0.1 to 0.95. This might be associated with the nature of the conductive polymers having a pi-conjugated system where the delocalization of carbonium charges would lower the ionic polarity and hydrophilicity of the polymeric chains.