A plenum chamber for a patient interface, the plenum chamber being pressurisable to a therapeutic pressure of at least 6 cmH2O above ambient air pressure, the plenum chamber comprising: one or more walls at least partially enclosing a volume of space; one or more plenum chamber inlet ports sized and structured to receive a flow of air at the therapeutic pressure for breathing by a patient; a seal-forming structure constructed and arranged to form a seal with a region of the patient's face surrounding an entrance to the patient's airways, said seal-forming structure having one or more holes therein such that the flow of air at said therapeutic pressure is delivered to an entrance to the patient's nares and to the patient's mouth via the one or more holes, the seal-forming structure constructed and arranged to maintain said therapeutic pressure in the plenum chamber throughout the patient's respiratory cycle in use; wherein the seal-forming structure comprises a nasal portion comprising a central portion configured to form a seal to an inferior periphery of the patient's nose surrounding the patient's nares and to the lip superior in use, and wherein the seal-forming structure does not lie over a nose ridge region of the patient's face; wherein the seal-forming structure comprises a pair of superior-facing intermediate portions configured to be located proximate to the patient's ala in use, the seal-forming structure having a greater thickness in the superior-facing intermediate portions than in the central portion; wherein the seal-forming structure comprises a pair of lateral-facing posterior portions on lateral non-patient facing regions of the nasal portion, the lateral-facing posterior regions comprising a greater thickness than the superior-facing intermediate portions. one or more walls at least partially enclosing a volume of space; one or more plenum chamber inlet ports sized and structured to receive a flow of air at the therapeutic pressure for breathing by a patient; a seal-forming structure constructed and arranged to form a seal with a region of the patient's face surrounding an entrance to the patient's airways, said seal-forming structure having one or more holes therein such that the flow of air at said therapeutic pressure is delivered to an entrance to the patient's nares and to the patient's mouth via the one or more holes, the seal-forming structure constructed and arranged to maintain said therapeutic pressure in the plenum chamber throughout the patient's respiratory cycle in use; wherein the seal-forming structure comprises a nasal portion comprising a central portion configured to form a seal to an inferior periphery of the patient's nose surrounding the patient's nares and to the lip superior in use, and wherein the seal-forming structure does not lie over a nose ridge region of the patient's face; wherein the seal-forming structure comprises a pair of superior-facing intermediate portions configured to be located proximate to the patient's ala in use, the seal-forming structure having a greater thickness in the superior-facing intermediate portions than in the central portion; wherein the seal-forming structure comprises a pair of lateral-facing posterior portions on lateral non-patient facing regions of the nasal portion, the lateral-facing posterior regions comprising a greater thickness than the superior-facing intermediate portions.