Abstract: A nasal interface device for use in the nares of a patient for positive airway pressure applications includes a pair of nasal prongs, each prong having a bore, a first end, a second end, and at least one deformable flap disposed proximate to the first end of each prong. The device further includes a body having a distal portion and a proximal portion forming a chamber, the proximal portion having apertures to receive the second ends of the nasal prongs, the chamber being in communication with the bores of the nasal prongs, and at least one exhalation port disposed within the body. The device includes at least one gas inlet on the distal portion of the body, the at least one gas inlet in communication with the chamber. In one preferred aspect of the invention, the at least one flap is deformable within the nares of a patient thereby creating a substantially airtight seal.