The compaction of composite preforms and the flow of resin through the fibrous network take place simultaneously during the Resin Film Infusion process. An experimental device, set up to impose combinations of hydraulic and mechanical loadings (Hydro-Mechanical loadings) to fibrous preforms is used to evaluate the transverse permeability in a continuous manner using different compression speeds for a glass satin weave and a carbon non crimped fabric. The transverse continuous permeability curves of the two fibrous reinforcements evaluated using fast compression speeds are not similar to the ones evaluated using low velocity. The fast compression speed permeability curve is the result of transient phenomena acting on the measured pressure. It therefore reflects the instantaneous permeability behaviour of the reinforcements. This may improve the accuracy of the permeability used to model processes such as RFI where the compression speed is not constant.