Each Level 4 Nipple provides the same consistent flow rate, so both you and baby know exactly what to expect. Together with the anti-colic internal vent system, the Level 4 Nipple offers vacuum-free feeding clinically proven to reduce colic, spit-up, burping and gas, better preserves nutrients, and aids in digestion for a good night?s sleep. Made of super-soft, high-grade silicone, the Level 4 Nipple fits all Dr. Brown?s Narrow bottles. The suggested age range for the Level 4 nipple is 9 months+, but baby?s preferred flow rate may vary. Dishwasher (top rack) and sterilizer safe. BPA free.