Accurate determination of the effective thermal conductivity of gas diffusion layers used in polymer electrolyte membrane fuel cells is very critical for efficient thermal and water management. In this paper, effective thermal conductivity of a diffusion medium material with and without polytetrafluoroethylene (PTFE) was estimated using a fractal approach. Fractal dimensions were obtained using the measured pore size distributions of the samples. The predicted through-plane thermal conductivities were in good agreement with the experimentally measured data. It was demonstrated that such a fractal technique can be employed, with slight modifications, to estimate in-plane thermal conductivity. Besides, application of a random multifractal simulation to obtain the required tortuous fractal dimension is introduced, which can be helpful in the absence of scanning electron microscopy images. It was shown that the tortuous fractal dimension obtained is in good agreement with the reported value in the literature. Finally, variation of the tortuous fractal dimensions with PTFE contents was also determined, which is of practical importance when estimating thermal conductivity of diffusion media with different amount of PTFE contents. Copyright (C) 2011 John Wiley & Sons, Ltd.