The AFB Platinum MERV 13 furnace / air filter is a best in class, hospital grade filter. The Platinum filter by FilterBuy offers the best level of filtration possible while still allowing a traditional residential or business HVAC unit to function efficiently. The AFB Platinum filter removes very fine particles from the air in your home, as well as potential allergens like mold, pet dander, bacteriaóeven particles that carry viruses. We recommend the AFB Platinum filter for use by homes or offices occupied by people suffering from asthma or other respiratory illness. Whenever you are choosing an air filter, make sure that you compare the nominal and actual size of the furnace filter that you are replacing. In this case, the ?nominal? size of the filter is 17x20x4 while the ?actual? size of the filter is 16.5 x 19.5 x 3.75. Generally, the nominal size is rounded and in bigger print while the actual size is in smaller print and in parenthesis to the side. The AFB Platinum MERV 13 filter is designed to last 3 months, or 3 times the average fiberglass filter. Each quantity purchased is for a pack of 6 filters. Note that AFB filters come in AFB Bronze (Merv 6), AFB Silver (Merv 8), AFB Gold (Merv 11), and AFB Platinum (Merv 13). The most commonly used filter for home or business use is the AFB Silver (Merv 8). If you have pets or allergies we recommend the AFB Gold (Merv 11). If you have asthma or other respiratory illness, we recommend the AFB Platinum (Merv 13). FilterBuy: Breathe Better!