A cushion includes a substantially triangularly shaped frame from which extends a membrane. The frame has a scalloped edge by which the cushion is affixed to a mask body. The membrane has an aperture into which the wearer's nose is received. The membrane is spaced away from the rim of the frame. The wearer's nose is received through the aperture into the chamber within the mask body. The shape of the seal forming portion is particularly suited to effectively seal the difficult region of the facial contour that is the crease between the sides of the nose and the face.