Individual bundles of ceramic fibers were infiltrated with SiC to study the reaction and diffusion kinetics during isothermal chemical vapor infiltration (CVI). More uniform infiltration was observed in samples where baffles were placed in the reactor and when HCl was added to the inlet gases. The evolution of the microstructure was modeled using an analytical expression for impinging cylindrical fibers. The transport of reactants was treated using classical descriptions of molecular and Knudsen diffusion in a porous body and also by considering the existence of a percolation threshold. All of these models predict that infiltration should be more uniform than the results that were obtained experimentally. It is possible that this discrepancy occurs because mass transport is more complex than the descriptions that were used. However, a more likely explanation is that the deposition kinetics are significantly more complex than the simple first-order reaction that was used for these models.