This combination filter has 3 levels of filtration to defend against flu viruses and pollutants in the air All-in-one filter system combines a 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 6 – 8 months and the Allergy & Flu Carbon Filter every 3 – 4 months (depending on usage). Change indicator light is displayed on your air purifier when filters need to be replaced. Compatible with all TruSens Z-2000 Air Purifiers.