Your HVAC filter isn't stopping fine dust and particulates — the fine particles that settle on furniture, show up in sunlight, and aggravate allergies every time the system runs. A standard filter catches the big stuff; fine dust goes right through and accumulates in your ductwork and on your lungs. 14 x 20 x 1 inch Filtrete Dust Reduction filter, MPR 600. The MPR (Microparticle Performance Rating) system tells you what particle size the filter captures — MPR 600 is optimized for fine dust, lint, and common indoor particulates. Electrostatic filter media adds an electric charge to standard mechanical filtration, improving capture of smaller particles without restricting airflow the way thicker or denser filter materials can. Fits standard 14x20x1 residential filter slots — the most common Stocked at Crofton Lumber and Akron Lumber.