ELECTRETIZED SHEET AND FILTER

Provided are an electret-treated sheet and a filter which have little reduction in chargeability after washing and little separation between sheets, and are excellent in water resistance. The electret-treated sheet comprises: a core layer (A) which is a porous film containing at least a thermoplastic resin; a surface layer (X) disposed on one side of the core layer (A); and a back surface layer (Y) disposed on the other side of the core layer (A), the surface layer (X) and the back surface layer (Y) each having a charged outermost surface, wherein the electret-treated sheet has a water vapor permeability coefficient of 0.1 to 2.5 g·mm/m2·24 hr; the core layer (A) has a pore aspect ratio of 5 to 50 and an average pore height of 2.5 to 15 µm; the surface layer (X) and the back surface layer (Y) each have a thickness of 5 to 200 µm; and the surface layer (X) comprises a heat seal layer (B) comprising the outermost surface, wherein the heat seal layer (B) has a melting point of 50 to 140°C.