Abstract: An electret filter made of a resin whose angle of contact upon wetting with pure water is no smaller than 95 degrees, as well as an electret filter made of a resin whose angle of contact upon wetting with pure water has been adjusted to no smaller than 95 degrees by addition of silicone oil. Those electret filters have high trapping efficiency and their ability to trap particulates, especially cigarette smoke, will not deteriorate even if they are continuously used. Therefore, they can advantageously be used as filter media in many applications such as home and industrial air conditioners, air cleaners, fan heaters, vacuum cleaners, and air conditioning systems for common equipment.