A patient interface for delivery of a supply of pressurised air or breathable gas to an entrance of a patient's airways includes a frame member, a cushion assembly provided to the frame member, and an anterior wall member repeatedly engageable with and disengageable from the cushion assembly. The frame member includes connectors operatively attachable to a positioning and stabilizing structure. The cushion assembly includes a seal-forming structure and a void defined by an anterior surface of the cushion assembly. The anterior wall member has a predetermined surface area to seal the void of the cushion assembly and form a gas chamber when the anterior wall member and the cushion assembly are engaged. The void of the cushion assembly is sized such that the patient's nose and/or mouth is substantially exposed when the anterior wall member is disengaged from the cushion assembly thereby improving breathing comfort of the patient.