The conventional transient plane source (TPS) method cannot accurately measure bulk thermal conductivity of thin films and coatings, because of the inclusion of thermal contact resistances in the results. In this study, a new modified TPS method is proposed that allows accurate measurement of bulk thermal conductivity of thin films and coatings. For this purpose, first, a hot disk testbed is used to measure the total thermal resistance for different thicknesses of a sample in the TPS test column. The bulk thermal conductivity is then deconvoluted from the results. Experiments have been performed on ethylene tetrafluoroethylene (ETFE) sheets, Nafion membranes, and gas diffusion layers (GDLs) with different thicknesses using the proposed method, and the results have been cross-checked with the data obtained from the guarded hot plate method, as per ASTM standard C177-13. The present modified TPS method yields thermal conductivity values of 0.174 +/- 0.002 W.m.m(-1).K-1 for ETFE and 0.243 +/- 0.007 W.m(-1).K-1 for Nafion, while the values measured by the guarded hot plate method are 0.177 +/- 0.002 W.m(-1).K-1 for ETFE and 0.214 +/- 0.003 W.m(-1).K-1 for Nafion. The GDL results, on the other hand, change with mechanical pressure, and about 15.7% difference is observed between the GDL results of the two methods. Overall, the developed method is proved to be highly reliable, quick, and accurate. (C) 2016 Elsevier Ltd. All rights reserved.