MaxMed in-line filter is attached between the machine's air out humidifier outlet and the CPAP hose. It functions by cleaning the intake air and preventing smaller particles from entering the CPAP during the sleep therapy. Heated hose the filter can be connected between the end of the heated hose and the short swivel hose for the mask. Simple to install and replace the machine end of the connection except the 22mm ID of the filter while the hose end connects to 22mm OD of the filter. Viral Filtration Efficiency (VFE) is 99.9% Bacterial Filtration Efficiency (BFE) is 99.9%