The present invention provides an interface that includes an inflatable envelope (that could also be referred to as a bag or balloon) having a supple wall structure. The inflatable envelope has a pair of locating protrusions that engage in the nostrils of the user. The locating protrusions supply gases flow to the user from inside the envelope. The envelope is so supple, and of sufficient dimension and shape, that when the inflated envelope is pressed against the face of a user, with the locating protrusions engaged in the nostrils of the user, the envelope contacts the surfaces of the user's face (the nose, the upper lip and the cheeks) and provides a seal.The interface further comprises a frame and a strap, the inflatable envelope is supported by the frame and the frame comprises connection points for connecting the strap to the frame, wherein, in use, the strap extends around the back of the user's head and provides pressure on the frame and helps seal the inflatable envelope to the user's face, the frame further comprises a pair of extended support members at a perimeter of the frame, the support members being located either side of the frame, and the inflatable envelope further comprises a pair of wing portions that, in use, are positioned directly under the support members.
