A patient interface for sealed delivery of a flow of air at a continuously positive pressure with respect to ambient air pressure to an entrance to the patient's airways including at least entrance of a patient's nares, wherein the patient interface is configured to maintain a therapy pressure in a range of about 3 cmH 2 O to about 40 cmH 2 O above ambient air pressure in use, throughout the patient's respiratory cycle, while the patient is sleeping, to ameliorate sleep disordered breathing, the patient interface comprising: a sealing structure to seal the patient interface against the patient's face, the sealing structure comprising: a sealing surface configured to form a seal around a periphery of the entrance to the patient's airways, and a loop that folds the sealing structure inwards of an outer perimeter of the sealing structure to form a substantially tube-shaped structure so that the loop is continuous, the loop comprising a portion of the sealing surface; a positioning and stabilising structure to maintain the sealing structure in sealing contact with an area surrounding an entrance to the patient's airways while maintaining a therapeutic pressure at the entrance to the patient's airways; a plenum chamber pressurised at a pressure above ambient pressure in use; and a gas washout vent configured to allow a flow of patient exhaled CO 2 to an exterior of the patient interface to minimise rebreathing of exhaled CO 2 by the patient, wherein the substantially tube-shaped structure comprises a hollow interior that is adapted to be in fluid communication with the pressure above ambient pressure; and wherein the substantially tube-shaped structure comprises two open ends. a sealing structure to seal the patient interface against the patient's face, the sealing structure comprising: a sealing surface configured to form a seal around a periphery of the entrance to the patient's airways, and a loop that folds the sealing structure inwards of an outer perimeter of the sealing structure to form a substantially tube-shaped structure so that the loop is continuous, the loop comprising a portion of the sealing surface; a sealing surface configured to form a seal around a periphery of the entrance to the patient's airways, and a loop that folds the sealing structure inwards of an outer perimeter of the sealing structure to form a substantially tube-shaped structure so that the loop is continuous, the loop comprising a portion of the sealing surface; a positioning and stabilising structure to maintain the sealing structure in sealing contact with an area surrounding an entrance to the patient's airways while maintaining a therapeutic pressure at the entrance to the patient's airways; a plenum chamber pressurised at a pressure above ambient pressure in use; and a gas washout vent configured to allow a flow of patient exhaled CO 2 to an exterior of the patient interface to minimise rebreathing of exhaled CO 2 by the patient, wherein the substantially tube-shaped structure comprises a hollow interior that is adapted to be in fluid communication with the pressure above ambient pressure; and wherein the substantially tube-shaped structure comprises two open ends.