A nasal seal, mask or an interface assembly have a seal body defining a breathing chamber. A nasal port is provided in the seal body. The nasal port has a central portion straddled by a pair of lateral portions. The nasal port further has an upper edge and a lower edge. The upper edge defines an inwardly projecting portion within the central portion. The lower edge defines an inwardly protection portion within the central portion. Thus, the nasal port can be generally bean-shaped or bowtie-shaped. The mask can include a frame having a central portion that supports the seal and a pair of arm portions that extend rearwardly of the seal and are configured to connect to headgear. The central portion can be more rigid than the arm portions. The mask can be configured to reduce noise transmitted through a bias flow vent.