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Electric charging of nonwoven materials employed as filter media improves their particle collection efficiency by the electrostatic particle capture mechanism that enhances the conventional mechanical filtration without causing an increase of the pressure drop. The aim of this paper is to provide a better understanding of the corona-charging process of such materials, by analyzing some of the factors that affect the repartition of the electric potential at the surface of the respective media. The experiments were carried out on two types of polypropylene samples: nonwoven fabrics and films. The experimental results show that the area occupied by the charge increases with both the charging voltage to the corona electrode and the duration of the charging process. The same area increases also with the time elapsed from the end of the charging, which points out the charge redistribution at the surface of the media by a surface conduction mechanism.