This filter with activated carbon pellets offers a level of defence against unwanted odours & VOC's that can invade your home. Specifically designed to remove these pollutants from the air this carbon layer is compatible with the Allergy and Flu HEPA filter drum for all Leitz TruSens Z-3000 / Z-3500 Large air purifiers. To keep your air purifier performing at its best it's recommended to replace the Allergy and Flu carbon filter every 3 months (depending on usage)