A subnasal sealing cushion for a patient interface device structured to deliver a flow of breathing gas to an airway of a user, comprising: a cushion member (20, 70, 80, 90, 100, 110, 120, 130, 140, 150) having a front side and a rear side opposite the front side, the rear side being structured to face a face of the user responsive to the patient interface device being donned by the user, the cushion member including: a support portion having an outer wall and a support structure (56a, 56b, 72, 82, 92, 102, 112, 122, 132, 142) coupled to the outer wall and extending longitudinally along a first direction, the first direction extending from the front side to the rear side, and a sealing flap portion coupled to the support portion, the sealing flap portion including a nasal shelf portion, the nasal shelf portion defining a nasal orifice and being structured to contact a bottom of a nose of the user to create a seal therewith responsive to the patient interface device being donned by the user, wherein the support structure is positioned under and spaced from a bottom of the nasal shelf portion, characterised in that the support structure comprises a number of ribs (60a, 60b, 74, 84, 94, 106, 114, 124, 134, 144), each of the ribs being coupled to and extending from the outer wall and extending longitudinally along the first direction. a cushion member (20, 70, 80, 90, 100, 110, 120, 130, 140, 150) having a front side and a rear side opposite the front side, the rear side being structured to face a face of the user responsive to the patient interface device being donned by the user, the cushion member including: a support portion having an outer wall and a support structure (56a, 56b, 72, 82, 92, 102, 112, 122, 132, 142) coupled to the outer wall and extending longitudinally along a first direction, the first direction extending from the front side to the rear side, and a sealing flap portion coupled to the support portion, the sealing flap portion including a nasal shelf portion, the nasal shelf portion defining a nasal orifice and being structured to contact a bottom of a nose of the user to create a seal therewith responsive to the patient interface device being donned by the user, wherein the support structure is positioned under and spaced from a bottom of the nasal shelf portion, a support portion having an outer wall and a support structure (56a, 56b, 72, 82, 92, 102, 112, 122, 132, 142) coupled to the outer wall and extending longitudinally along a first direction, the first direction extending from the front side to the rear side, and a sealing flap portion coupled to the support portion, the sealing flap portion including a nasal shelf portion, the nasal shelf portion defining a nasal orifice and being structured to contact a bottom of a nose of the user to create a seal therewith responsive to the patient interface device being donned by the user, wherein the support structure is positioned under and spaced from a bottom of the nasal shelf portion, characterised in that the support structure comprises a number of ribs (60a, 60b, 74, 84, 94, 106, 114, 124, 134, 144), each of the ribs being coupled to and extending from the outer wall and extending longitudinally along the first direction.