Built for large residential returns, this 24 x 24 x 1-inch Filtrete Allergen Defense filter uses pleated electrostatic media with 3‑in‑1 technology to clean recirculated air in your furnace or central AC system. With a 1000 MPR (MERV 11) rating, it is engineered to attract and capture microscopic particles like pet dander, smoke, and smog, along with larger allergens such as lint, household dust, pollen, and mold spores.