The possibility of using positrons to study electret has been investigated. The different shapes in the angular correlation curves for aluminum, wax mixture and electret have been compared with those curves for metallic elements, ionic crystals and insulators observed by Lang and de Benedetti. The proposed angular correlation comparison method seems to reveal some information on the physical mechanism of heterocharge formation in electrets and to confirm that the internal persistent electric polarization arises from an ionic mechanism, instead of a true dipole mechanism.