A respiratory mask (10), particularly of the type used in CPAP treatment, has a gas washout vent (26,28). In one embodiment the vent (26,28) is made of a thin air-permeable membrane (28). Generally, the membrane (28) is thinner than about 0.5 mm. The membrane (28) can be made of a hydrophobic material such as polytetrafluoroethylene (PTFE). The membrane (28) can also be fabricated from expanded PTFE. In an alternative embodiment, the vent assembly includes a vent constructed from stainless steel.
