Abstract: The present invention provides a gas-delivery system for delivering breathable gas to a subject, comprising a source of pressurised gas, a mask cushion, a means for positioning the mask cushion for delivery of gas, and a filter for filtering particles from exhaled air. Preferably, the filter filters exhaled air only. The filter may engage a mask frame on any suitable surface of the frame in relation to the mask cushion.

Abstract: The invention provides a nasal cushion for a mask assembly for delivering pressurised gas to the nose of a subject for treatment with continuous positive air pressure. The nasal cushion includes a self-supporting side wall defining a nose-receiving cavity; the side wall extending from a first end to a second end. The side wall is formed continuously with a thin membrane extending inwardly from a second end of the side wall into the nose-receiving cavity for sealingly engaging the nose, upper lip and cheeks of a subject. The side wall has continuously varying thickness. The first end of the side wall is adapted to engage a mask frame. The invention further provides a mask assembly for delivering pressurised gas to a patient, the assembly including a nasal cushion for sealing against the nose, cheek and-lip area the nasal cushion as described, a frame for receiving the nasal cushion, and a headgear, the headgear including a rigid arm for positioning behind the ear of a patient.