A cushion assembly for 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 4 cmH2O to about 30 cmH2O above ambient air pressure in use, throughout the patient's respiratory cycle, while the patient is sleeping, to ameliorate sleep disordered breathing, the cushion assembly comprising: an elastomeric support portion; an elastomeric seal-forming structure supported by the elastomeric support portion and being shaped to be bisected by a sagittal plane that includes a line tangent to the elastomeric seal-forming structure at a superior tangent point and at an inferior tangent point, the elastomeric support portion being more rigid than the elastomeric seal-forming structure; and a chamber defined by the elastomeric support portion and the elastomeric seal-forming structure, wherein the elastomeric seal-forming structure comprises an inner surface forming a boundary for the chamber and comprises an outer surface opposite the inner surface, wherein the elastomeric seal-forming structure comprises a first compliant region that includes the superior tangent point, a second compliant region separated from the first compliant region by a support region that is more rigid than the first and second compliant regions, wherein the second compliant region is configured to seal against a side of the patient's nose when the cushion is mounted to the patient's face, wherein the more rigid support region is configured to resist crinkling and/or creasing of the first compliant region when the first compliant region is subject to a compressive force, and wherein for every point in the rigid support region, the inner surface has a negative curvature when the outer surface has a positive curvature and the inner surface has a positive curvature when the outer surface has a negative curvature, characterized in that the more rigid support region extends to and is anchored by the elastomeric support portion, and the support region increases in rigidity toward the elastomeric support portion. an elastomeric support portion; an elastomeric seal-forming structure supported by the elastomeric support portion and being shaped to be bisected by a sagittal plane that includes a line tangent to the elastomeric seal-forming structure at a superior tangent point and at an inferior tangent point, the elastomeric support portion being more rigid than the elastomeric seal-forming structure; and a chamber defined by the elastomeric support portion and the elastomeric seal-forming structure, wherein the elastomeric seal-forming structure comprises an inner surface forming a boundary for the chamber and comprises an outer surface opposite the inner surface, wherein the elastomeric seal-forming structure comprises a first compliant region that includes the superior tangent point, a second compliant region separated from the first compliant region by a support region that is more rigid than the first and second compliant regions, wherein the second compliant region is configured to seal against a side of the patient's nose when the cushion is mounted to the patient's face, wherein the more rigid support region is configured to resist crinkling and/or creasing of the first compliant region when the first compliant region is subject to a compressive force, and wherein for every point in the rigid support region, the inner surface has a negative curvature when the outer surface has a positive curvature and the inner surface has a positive curvature when the outer surface has a negative curvature, characterized in that the more rigid support region extends to and is anchored by the elastomeric support portion, and the support region increases in rigidity toward the elastomeric support portion.