The uniquely designed Dr. Brown’s Narrow Neck Level 3 Teat is a medium-fast flow nipple, made for use with thinner liquids, ideal for babies who are 6 months+ old or are pros at bottle feeding. Designed alongside medical professionals, the correctly contoured teat shape and high-grade, soft silicone offer a more comfortable feeding experience for baby. Together with the anti-colic internal vent system, this teat gives baby vacuum-free feeding (air never mixes with the breast milk or formula), which is clinically proven to reduce colic. This leads to a decrease in spit-up, burping, and gas, better preserves nutrients, and aids in digestion for a good night’s sleep. Each same-level teat provides the same consistent, natural flow rate, so both you and baby know what to expect. These teats are uniquely engineered for Dr. Brown's narrow neck plastic and glass baby bottles, other teats won’t work with the patented vent system.