Electro-reflective properties in the mid-IR of a series of electropolymerized poly (3,4-ethylenedioxythiophene) (PEDOT) layers were studied in their doped and dedoped states and correlated to their morphology and electronic conductivity properties. The films were prepared on ITO electrodes using lithium perchlorate or lithium trifluoromethanesulfonate as supporting electrolyte and acetonitrile as solvent. In order to investigate the effect of the surface morphology, each side of the films was studied, i.e. either the smooth surface in contact with the ITO substrate during synthesis or the rougher surface in contact with the electrolytic medium which morphology varies with the polymerization charge density. For both salts, the IR reflectivity of doped films having similar electronic conductivity decreases drastically upon increasing surface roughness. This was attributed to enhanced absorption in the same way as reported for metallic surfaces. Therefore the full control of the morphology may improve the device optical properties in the IR range. In addition, whatever the electrolyte, the IR reflectivity is shown to follow the same trend as a function of the electronic conductivity varying over about five orders of magnitude. Furthermore, the electro-reflective behavior of PEDOT layers can be described by the Drude model provided the electronic conductivity exceeds 90 S cm(-1). By several aspects, these films have thus a quasi-metallic behavior. Finally, the highest and lowest reflectivity obtained in the 8-20 mu m range for these PEDOT layers is 67% and 21% respectively, which opens up interesting perspective in view of the elaboration of PEDOT-based devices with tunable IR electro-reflective properties. (c) 2015 Elsevier B.V. All rights reserved.