A device to reduce conduit rainout, the device comprising a gas conduit having an input aperture and an output aperture, the gas conduit configured as a channel (106) for movement of a breathable gas between the input aperture and the output aperture, the gas conduit being configured to provide the breathable gas from the output aperture to a patient interface, and a vapor barrier (150) operable to selectively prevent vapor passing from the patient interface through the gas conduit to the input aperture.