A respiratory pressure therapy system comprising: a patient interface comprising: at least one housing portion: a at least partially forming a plenum chamber pressurizable to a therapeutic pressure above ambient air pressure; a seal-forming structure constructed and arranged to seal with a region of the patient's face at or surrounding the patient's nares such that a flow of air at said therapeutic pressure is delivered to at least the patient's nares, the seal-forming structure constructed and arranged to maintain said therapeutic pressure in the plenum chamber throughout the patient's respiratory cycle in use; and a positioning and stabilising structure constructed and arranged to provide an elastic force to hold the seal-forming structure in a therapeutically effective position on the patient's head, the positioning and stabilising structure comprising a tie, a lateral portion of the tie being constructed and arranged to overlie a region of the patient's head superior to the otobasion superior in use, and a superior portion of the tie being constructed and arranged to overlie a region of the patient's head in a region of the parietal bone in use, wherein the positioning and stabilising structure has a non-rigid decoupling portion; a blower configured to pressurize the plenum chamber to the therapeutic pressure, the blower having a motor, the blower being connected to the plenum chamber such that the blower is suspended relative to the remainder of the patient interface by the plenum chamber; a power supply configured to provide electrical power to the blower; a vent assembly configured to discharge gas from the plenum chamber to atmosphere, the vent assembly having an open position to allow gas to be discharged to atmosphere through the vent assembly and a closed position to prevent gas from being discharged to atmosphere through the vent assembly; a sensor port positioned downstream of the vent assembly such that the sensor port is in pneumatic communication with the air within the plenum chamber in any position of the vent assembly; and a sensor in pneumatic communication with the air within the plenum chamber via the sensor port. a patient interface comprising: at least one housing portion: a at least partially forming a plenum chamber pressurizable to a therapeutic pressure above ambient air pressure; a seal-forming structure constructed and arranged to seal with a region of the patient's face at or surrounding the patient's nares such that a flow of air at said therapeutic pressure is delivered to at least the patient's nares, the seal-forming structure constructed and arranged to maintain said therapeutic pressure in the plenum chamber throughout the patient's respiratory cycle in use; and a positioning and stabilising structure constructed and arranged to provide an elastic force to hold the seal-forming structure in a therapeutically effective position on the patient's head, the positioning and stabilising structure comprising a tie, a lateral portion of the tie being constructed and arranged to overlie a region of the patient's head superior to the otobasion superior in use, and a superior portion of the tie being constructed and arranged to overlie a region of the patient's head in a region of the parietal bone in use, wherein the positioning and stabilising structure has a non-rigid decoupling portion; at least one housing portion: a at least partially forming a plenum chamber pressurizable to a therapeutic pressure above ambient air pressure; a seal-forming structure constructed and arranged to seal with a region of the patient's face at or surrounding the patient's nares such that a flow of air at said therapeutic pressure is delivered to at least the patient's nares, the seal-forming structure constructed and arranged to maintain said therapeutic pressure in the plenum chamber throughout the patient's respiratory cycle in use; and a positioning and stabilising structure constructed and arranged to provide an elastic force to hold the seal-forming structure in a therapeutically effective position on the patient's head, the positioning and stabilising structure comprising a tie, a lateral portion of the tie being constructed and arranged to overlie a region of the patient's head superior to the otobasion superior in use, and a superior portion of the tie being constructed and arranged to overlie a region of the patient's head in a region of the parietal bone in use, wherein the positioning and stabilising structure has a non-rigid decoupling portion; a blower configured to pressurize the plenum chamber to the therapeutic pressure, the blower having a motor, the blower being connected to the plenum chamber such that the blower is suspended relative to the remainder of the patient interface by the plenum chamber; a power supply configured to provide electrical power to the blower; a vent assembly configured to discharge gas from the plenum chamber to atmosphere, the vent assembly having an open position to allow gas to be discharged to atmosphere through the vent assembly and a closed position to prevent gas from being discharged to atmosphere through the vent assembly; a sensor port positioned downstream of the vent assembly such that the sensor port is in pneumatic communication with the air within the plenum chamber in any position of the vent assembly; and a sensor in pneumatic communication with the air within the plenum chamber via the sensor port.