Allergen filter. 20 in. x 25 in. x 4 in. High-efficiency filter for home forced-air heating and cooling systems with electrostatically charged fibers that capture airborne microparticles (0.3 to 1 micron in size) such as smoke, pollen, mold spores, pet dander, dust and lint. Performance rating of MERV 11 or MRP 1550. "Filtrete" filters reduce up to 30 times more particles than ordinary fiberglass filters.