The present invention describes a mask system for delivering pressurized breathable gas to a patient, comprising a chamber forming portion including: a back panel at least partially delimiting a cavity adapted to receive a patient's nose, the back panel including an upper panel coupled to a lower panel such that an opening is formed between the upper panel and the lower panel, the opening configured such that the patient's nose is received into the cavity through the opening, wherein the upper panel has an upper seal portion configured to seal against the patient's external nares, and the lower panel has a lower seal portion configured to seal against the patient's upper lip.
