2 per box  Pura's feeding systems are not only the safest in the world but our  new Natural Vent Nipple was designed to mimic the variable flow  rate of breast feeding.   These new nipples, designed over the past year by the Pura team,  employ a new shape that promotes a better seal between the baby  and the nipple, an elongated vent to reduce colic and spit-ups, and  the use of multiple holes in the tip to achieve different flow rates.