Preparation of core-shell particles consisting of polystyrene-poly(ethylene glycol) monomethacrylate (PS-PEGMA) core covered with polypyrrole (PPy) shell is described. The thickness of PPy shell, which strongly influences electrical properties of the films prepared from the particles, can be varied by changing pyrrole load, controlling the overall template surface area in the system and by influencing the pyrrole polymerization kinetics in the presence of different oxidants. The type of anions and PPy loading strongly influence the electrical conductivity. Typical value of the resistivity of thin film consisting of core-shell particles was 34 Omega m (PPy oxidized by FeCl3, shell thickness 3 nm). Current-voltage dependences of low conductivity samples (thin PPy shell layer) are characteristic of contact-limited currents. The conductivity of the particles changes with humidity, which can be utilized in humidity sensors. (C) 2008 Elsevier Ltd. All rights reserved