Electret filter

PURPOSE:To provide the electret filter of small pressure loss and high dust collection effect, by continually bending a high-molecular film already changed into the electret. CONSTITUTION:The high-molecular film of polyolefin resin, polyester resin or the like is changed into an electret film 1 by a thermoelectret process or the like. The electret film is continually bent or folded so that creases 2 are made. Such creased films 1 are stacked in the direction of their thickness. The edges of the creases of the stacked films are bonded or fused so that a stacked piece 5 is provided. This stacked piece is used as the electret filter. Since the area of contact of the electret films with air is large and the pressure loss through the filter is small, its dust collection performance is excellent and its lifetime is long.