Quantity of Four 20 Inch Square Furnace Air Filters For One Inch Slots Four Safe Home TM Duo 20 by 20 by 1 inch furnace filters a year's supply for most families. Safe Home Duo MERV 8 furnace panel filters are the only one inch thick home air replacement filters to capture allergens, odors, and harmful chemicals. Duo's superior design includes self sealing edges to maximize effectiveness at capturing allergens, odors, and chemicals from the air in your house. Uses include furnace filter slots, temporary needs, or custom sizes in air return grills. The Duo replaces any 1 thick home air filter in any location and can last up to 3 months. Always check with your HVAC technician before changing from your current furnace filter. This unit is a MERV 8. Made in USA. How does the Duo work? The polyester outer layers remove pollen, mold spores, and other common allergens. The inner layer features FormaldaSorb TM and activated carbon that traps a variety of odors and hazardousgasses, such as formaldehyde, ammonia, and others that are emitted by cleaning chemicals, paint, particle board, and other household items. No other filters are as effective at removing dust mites, mold spores, pollen, odors, cleaning chemicals, ozone, paint fumes, and common gasses like formaldehyde which triggers asthma and allergies. Safe Home Duo Filter Features Dimensions 20 x 20 x 1 Package of 4 furnace filters Captures up to 95% of common household allergens Eliminates odors from pets, paint, cooking, and more FormaldaSorb TM , a patented potassium permanganate product plus the activated carbon in the second layer of the filter trap gasses that can cause health issues. Highly effective and affordable. 2 stage air filter one MERV 8 rated polyester white allergen filter plus the activated carbon filter pad. Made in USA. Change the Duo at least every 3 months. Some conditions that feature pets, construction work, painting or smoking may produce more pollutants and This item ships from a separate warehouse and may require extra time for delivery.