Lu et al.＇s modeling of gas-solid reaction demonstrated the significant influence of mass transfer on the global transformation of consolidated porous reactive media with reactive gas at low pressure and low permeability: Their model coupled mass transfer with chemical kinetics at the grain level and heal transfer with mass transfer at the pellet level. The comparison between simulation results and recent experiments demonstrated that the value of the material permeability varies during the reaction process This study presents the permeability decrease during the synthesis process. A correlation representing the nonlinear evolution of permeability was identified for different reactive materials used for experiments. These mechanisms salt satisfactorily explain both the experimental measurements of global advancement and local temperature profiles.