Dr. Brown's Natural Wide-Neck Nipple - Level 4 (9m+) - 6 pack Key Features: 100% Silicone Patented internal vent system helps reduce colic, spit-up, burping and gas Positive pressure design allows babies to feed comfortably, because the vent system eliminates the air bubbles and vacuum All parts are dishwasher safe Wide-Neck Nipples Level Four are ideal for babies 9+ months. Dr. Brown's BPA Free Nipples reduce colic, vomiting, reflux, burping, and gas. Prevents air bubbles from forming in milk or formula. Helps reduce fluid in the ear. Prevents nipple collapse.