Filtrete 18"x18"x1" Red Micro Allergen Filter. It is 90% effective at capturing large allergens like mold spores & pet dander. Electrostatically charged to capture microscopic allergens like dust, smoke & smog, it also captures bacteria & particles that can carry viruses. Meeting the guidelines of the American Lung Association Health House Program, this MPR 1000 filter lasts up to 3 months.