The paper summarizes measurements in which both external electric field (applied by electrodes at the fabric surface) and flyash electrical charge (controlled by an upstream corona precharger) are independent variables in a factorial performance experiment carried out in a laboratory pulse-jet baghouse. The observations suggest that the mechanism by which the external field enhances the performance of the fabric filter is increasing the permeability of the collected flyash layer, while the precharger enhancement mechanism is primarily that of a prefilter. Since the magnitude of the electrical charge/mass of the test flyash does not affect the magnitude of the enhancement induced by the external electric field, the enhancement mechanism by which the external field increases the dust cake permeability is concluded not to be a coulomb capture force.