The development and characterisation of new PPy composites has been carried out using direct addition of polypyrrole (PPy) powders to polymeric substrates and in situ polymerisation in order to develop workable composites with conductivities similar to that of oxidised PPy. Precipitation, dispersion and emulsion polymerisation techniques were used in the development of PPy fillers. Electron microscopy, differential light scattering (DLS), nitrogen adsorption surface area analysis and conductivity measurements were used to determine the physical properties of PPy powders produced with ferric chloride oxidant. Powders possessing approximately 380-1400nm effective particle diameters, 8-50m2 surface areas and 0.001-1S/cm conductivities were produced. Physically mixed composites were produced by adding PPy powders to Surlyn ionomer, styrene ethylene butylene styrene triblock copolymers (SEBS) and nitrile butadiene rubber (NBR) hosts. Changes in physical properties (including tensile strength and electrical conductivity) of PPy and carbon black filled composites were also studied and compared. In situ polymerisation-based composite development of PPy composites with higher conductivities than obtained using physical mixing techniques (&lt10-4S/cm) was carried out. Sequential treatments with monomer and oxidant were used to test the combination of polymer host (including those described above) and reaction media (including tetrahydrofuran, diethyl ether and acetonitrile). Examination of PPy penetration and content (using optical microscopy and gravimetric analysis) showed a diethyl ether reaction media and SEBS host were suitable for further PPy Abstract composite development. The simultaneous diffusion polymerisation (SDP) technique, which involves treating opposite sides of host sheets with separate monomer and oxidant solutions, was employed to form PPy- SEBS composites. The layered morphology of SDP-formed composites was characterised by techniques including X-ray imaging, Raman mapping and electron probe microchemical analysis; and a PPy growth mechanism proposed. Optimisation of PPy composite properties was carried out using a central composite factorial design (varying reagent concentrations, reaction temperatures and reaction times) with conductivities of approximately 1S/cm achieved, Properties of PPy composites formed using physical mixing and SDP techniques were compared. Preliminary investigations (using electron and atomic force microscopy) were carried out to develop core-shell PPy composites that possess a continuous PPy component rather than the layered morphology associated with reductions in tensile strength.