Ultra Allergen Pleated Filter, 3-Month, Purple, 12 x 20 x 1-In.12" x 20" x 1", purple, ultra allergen filtrete pleated filter, 3 month filter is 90% effective at capturing large allergens like mold spores & pet dander, electrostatically charged, captures microscopic allergens like dust, smoke & smog, captures bacteria & particles that can carry viruses, meets the guidelines of the american lung association health house program, mpr rating 1500, lasts up to 3 months.