Use Filtrate 16 in. x 20 in. x 1 in. Allergen Plus FPR 8 Air Filters (2-Pack) to stop pollen, mold spores and other allergens from getting into your home's ductwork. Each electro statically charged filter is dependable for up to 3 months. electro statically charged fibers attract and capture smoke, pet dander, household dust and smog.