20" x 30" x 1", red, micro Allergen FILTRETE filter, 3 month filter is 90percent 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 1000, lasts up to 3 months.