Designed For Seamless Transition Between Bottle and Breast: Natural Start bottles have silicone nipples that are designed with an anti-colic valve and mimic the flexibility of a breast Natural Latch For Baby: Our silicone bottle nipples are shaped to encourage a natural latch, reducing air intake and preventing nipple confusion when switching between breast, bottle and back again 100% Leakproof Bottle to Avoid Messes: When the screw ring, nipple and cap are all secured, your baby bottle is completely mess-free and 100% leakproof, even if it's turned upside down Designed For Pace Feeding: The soft silicone nipple flexes and stretches like a breast and allows your baby to feed comfortably at their own pace and stop when full Self-Sterilizing Bottles: Tommee Tippee anti-colic bottles can be easily self-sterilized in just three minutes making cleaning quick and convenient for busy moms