The Stratus 5 HEPA Paper Filter is an internal filter that filters out superfine particles in the Stratus 5 Oxygen Concentrator's air flow. It must be in place at all times while the concentrator is in use. The HEPA filter is disposable.
The Stratus 5 HEPA paper filter is located in the back of the unit. . The unit comes with one HEPA filter. This filter should be changed every 10,000 hours.