This activated carbon pellet filter is specifically designed to remove pollutants from the air that can trigger allergies or cause flu-like symptoms | This carbon layer fits with Allergy & Flu Filter drum for all TruSens Medium Air Purifiers | This filter with activated carbon pellets offers a level of defence against unwanted air pollutants that can invade your home | This layer is what needs to be replaced on the Allergy & Flu HEPA drum filter | Filter replacement is essential for your air purifier to perform at its best | For best results, replace carbon filter every 3 - 4 months | Change indicator light is displayed on purifier when filter needs to be replaced | Fits with the Allergy & Flu Filter drum for all TruSens Medium Air Purifiers | Pack includes 1 filter