The aim of this work was to develop a procedure for the application of pulsed thermography as a quantitative method for porosity determination in carbon fibre reinforced polymers. Mathematical models are used to link the microstructural properties with global thermal properties which are the observation time and the thermal diffusivity. These detailed mathematical models, based on the effective medium theory, can be simplified for practical applications in the industry. It is possible to calculate a porosity image by the measurement of the thermal diffusion time. The predicted porosity image matches the measured porosity image based on cone beam X-ray computed tomography reference measurement quite well.