Vacuum vapour phase polymerization (VVPP) is a facile means of producing flexible PEDOT thin films having conductivities in excess of 1500 S cm(-1). The process is understood to utilize water as the effective proton scavenger during synthesis. The originating source of water, under vacuum condition however, was unknown. The location of the water within the oxidant solution was examined, with individual components desiccated and thermo-gravametric analysis (TGA) performed to ascertain the root source. The co-polymer PEG-PPG-PEG provides some water, while the majority originates from coordinated water associated with the iron tosylate oxidant, and from free water residing within the solvent carrier. Importantly, with the incorporation of the co-polymer water remains locked within the oxidant layer under vacuum and this allows the VVPP reaction to proceed without the need for an external water supply. Furthermore PEG-PPG-PEG serves the multi-functional role of inhibiting crystal formation within the oxidant layer, and reducing the effective reactivity of the oxidant. Finally, an examination of literature suggests that the choice of oxidant may depend on the type of VPP process used. (C) 2012 Elsevier Ltd. All rights reserved.