Abstract: The present invention is an improvement in electretized filtering means. This is an electric charge holding structure wherein the filter medium is covered on two opposite sides with an electrically conductive material having an air permeability that does not impair the air permeability of the filter and these two opposite sides are shorted together. This concept is similar to causing a short in the magnetic lines of force for the purpose of long time retention of the magnetic force as often employed in the vicinity of a permanent magnet. In this invention this idea is applied to electret as an air-filter medium.