A CPAP system for supplying humidified gases to a user is disclosed in which various interfaces are described for gas delivery. A mask cushion including a deformable cushion and thin sheath is described. A forehead rest with a horizontal pivot that is attached to the mask is disclosed. An outlet vent to reduce the noise from exhausted carbon dioxide is described. A mouthpiece is also described with an outlet diffuser including Heat Moisture Exchanger Material.