The DuPont Allergy and Flu Anti-viral True HEPA Filter for TruSens Air Purifiers is a combination filter with three levels of filtration to defend against flu viruses and pollutants in the air. All-in-one filter system combines an anti-viral True HEPA filter with an activated carbon filter and a durable mesh prefilter. 360 degree filtration draws in air from all directions, collecting pollutants from around the room. The filter is at the core of purifying your air and replacement is essential for your purifier to perform at its best. Replace every 3 to 4 months (depending on usage). Change indicator light is displayed on your air purifier when filters need to be replaced. Compatible with TruSens Air Purifiers.