Filtrete 12"x24"x1" Red Micro Allergen Filtrete Filter. This filter is 90% effective at capturing large allergens like mold spores and pet dander, and it is electrostatically charged to capture microscopic allergens like dust, smoke, and smog. It also captures bacteria and particles that can carry viruses, meeting the guidelines of the American Lung Association Health House Program. With an MPR rating of 1000, this filter lasts up to 3 months.