Gaining a deeper understanding of the growth of poly(3,4-ethylenedioxythiophene) (PEDOT) films by vapour phase polymerisation (VPP) is essential for the rational design and optimization of such films. The VPP process was used to synthesise films of PEDOT on oxidant-coated substrates. Atomic force microscopy images showed that the morphology of the films changed considerably with time. Utilising a quartz crystal microbalance with dissipation measurement (QCM-D), we found that the kinetics of polymerisation and the viscoelastic properties of the films varied. The data reveal four distinct stages in film growth. Each stage produces a layer having different conductivity values, from a low of 276 S cm(-1) to a high of 1196 S cm(-1). Conductivity and electrochromic optical contrast, Delta%Tx, can thus be maximized by appropriate termination of the polymerisation reaction. Factors determining the polymerisation rate and changes in conductivity and optical performance are discussed. (C) 2010 Elsevier Ltd. All rights reserved.