The paper gives results of an evaluation of the effect of loading dust type on the filtration efficiency of electrostatically charged filters. Three types of filters were evaluated: a rigid-cell filter charged using an electrodynamic spinning process, a pleated-panel filter charged using a corona charging process, and a residential filter charged using a split-fiber process. The filtration efficiency measurements covered a 0.3-10 micrometer diameter size range. Exposures consisted of outdoor ambient air, in-home air, American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRE) dust, ASHRAE dust without carbon black, and a sub-micrometer salt aerosol. Results show that all the ambient and in-home exposed filters had substantial decreases in filtration efficiency. The submicrometer salt aerosol came closest to duplicating the outdoor and in-home aerosol exposure results, although the magnitude of the efficiency decrease was underestimated in some cases.