Sized for smaller returns, this 12 x 20 x 1-inch Filtrete Allergen Defense filter is made with synthetic pleated media to help clean recirculated air in residential HVAC systems. With Filtrete 3‑in‑1 technology and a 1000 MPR (MERV 11) rating, it attracts and traps microscopic particles like smoke and smog along with larger allergens such as lint, household dust, pollen, mold spores, pet dander, and dust mite debris.