Filters made from electret media with quasi-permanent electrical charges have been widely applied to control particulate matter (PM) pollution. However, studies using parametric analysis to examine the effects of the operating face velocity, charge density, fiber diameter, porosity, and thickness on the energy efficiency of the filtration are lacking. A reliable parametric analysis requires an accurate filtration model. Without adding any empirical parameters, a modified model developed earlier by the authors was the first to accurately predict the efficiency of electret filters at different face velocities and with different filter charge densities for neutralized particles. To further verify the applicability of this model, we conducted filtration experiments in which singly charged, neutral, and neutralized monodisperse particles with 3–500 nm through two different electret filters, one with a charge density of 0.075 and the other with a charge density of 0.025 mC m–2, as well as through discharged electret filters. The results of the modified model agreed well with the experimental data. The validated model was then used to conduct the parametric analysis to clarify the effects of the aforementioned parameters on filter performance. It was found that the increase in efficiency due to the fibers’ charge states varied largely with the face velocity and the charge density of the electret. Furthermore, when the pressure drop was held constant, using thicker filters with less solidity reduced particle penetration. The results in this work can be applied to the design and operation of future electret filters.