As a part of the modelling of CVI (Chemical Vapour Infiltration), one of the processing techniques of Carbon - Carbon composites, a better understanding of the relation between fibre architecture and heat and mass transport properties is required. An excellent starting point for the pore-scale modelling of heat and gas transport is the acquisition of 3D images of the porous media through Computerised Micro Tomography. Such images have been acquired at different resolutions and two successive change-of-scale procedures have been performed to compute effective transport properties.