The present invention provides a vent assembly suitable for use with a respiratory mask of the type used in CPAP treatment. In one embodiment the vent is made of a thin air permeable membrane. Generally, the membrane is thinner than 0.5 mm. The membrane can be made of a hydrophobic material such as polytetrafluoroethylene...http://www.google.sh/patents/US6823865?utm_source=gb-gplus-sharePatent US6823865 - Respiratory mask having gas washout vent and gas washout vent assembly for respiratory mask
