18" x 20" x 1", Red, Micro Filtrete 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 1000, Lasts Up To 3 Months.