Fellowes DX55 Carbon Filter (Pack of 4) 9324101. Catches particles in the air to purify your atmosphere. Perfect for people with respiratory problems. Helps prevent the spread of disease. With normal usage filters should be replaced every 3 months.Ensuring that your air is as pure as possible, the AeraMax 20 is perfect for guaranteeing that there is a never a problem with dirty or unpleasant air. Working to catch larger particles from the air, you don't have to worry about any pollutants getting into your lungs. This filter works perfectly with your machine and will inform you when it is time to replace the filter, meaning that it never stops working without warning.