High-Grade Silicone: The teats are made of super-soft, high-grade silicone, ensuring durability and flexibility for long-lasting use. Precision Cut: Dr. Brown's teats are precision cut to allow for optimal performance and flow of liquid, ensuring smooth and consistent feeding. Two-Piece Internal Vent System: Dr. Brown's bottles feature a patented two-piece internal vent system that creates positive-pressure flow, similar to breastfeeding. This system fully vents the bottle for vacuum-free feeding. Vent System Functionality: As the baby feeds, air is channeled from the teat collar through the vent system, bypassing the breast milk or formula and traveling to the back of the bottle. This prevents air from mixing with the milk or formula, minimizing oxidation and preserving essential nutrients like vitamins C, A, and E. Reduction of Feeding Problems: By eliminating vacuum and air bubbles, the vent system reduces common feeding problems such as colic, burping, and wind. Babies can feed more comfortably without discomfort. Prevention of Teat Collapse: The vent system ensures that the breast milk or formula flows freely without teat collapse, providing a consistent feeding experience for your baby. Overall, the Dr. Brown's Narrow Neck Teats Level 4 offer a reliable and effective solution for parents seeking to minimize feeding issues and provide a comfortable feeding experience for their baby.