A prong for use in nasal ventilation therapies featuring a dome-shaped resilient flexible foam member that locates in the nostril socket, more effectively distributing sealing contact pressure for a range of nose morphologies, akin to a ball and socket. A nasal cannula 20 extending from base 22 through spherical foam sleeve 23 provides a stiffened lumen for ventilation gas transport. Foam member 23 may have a compressible flange 24, which elastically engages with a nostril's internal sill feature. The foam member may have a second compressible flange 26 at its base, which shields the patient's skin from direct contact by the stiffer structure of the combination gas delivery device. Dissimilarly sized or shaped or rotationally oriented left-right prong halves may be combined. The foam member may be divided at the midline, along a thinned section 27. A plurality of foam prongs may be packed on to a common carrier (42, see figures 12, 13) and have a detachable selection gauge (36, see figure 13) or information instrument.
