Patient interface with a seal-forming structure having varying thickness

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 a patient's airways including at least entrance of the 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 and 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 more rigid support region extends to and is anchored by the elastomeric support portion, and wherein for every point in the rigid support region, a curvature of the inner surface follows a curvature of the outer surface,
• wherein the outer surface of the elastomeric seal-forming structure in the first compliant region is saddle-shaped, wherein at least a portion of the outer surface of the elastomeric seal-forming structure in the second compliant region is dome-shaped, and wherein in the more rigid support region, the outer surface of the elastomeric seal-forming structure transitions from the saddle shape of the first compliant region to the dome shape in the second compliant region.