Vapour-phase chemical polymerization of pyrrole was investigated in which a cotton thread coated with FeCl3 oxidant was exposed to pyrrole vapour and the electrical resistance of this conductive polypyrrole supported on cotton thread was measured using a specially designed four-point probe. The relationships of the resistance of the polypyrrole supported on cotton thread with various experimental parameters such as concentrations of the oxidant and monomer, polymerization time, solvent effect and temperature were studied. It was found that the vapour-phase polymerization was a fast reaction. The resistance decreased with an increasing concentration of FeCl3 and polymerization temperature. The presence of some solvents such as water, hexane and toluene in the vapour phase did not affect the polymerization process. However, some solvents such as methanol and acetone were found to be unsuitable for this process.