NUK bottles feature improved Perfect Fit nipple, which is the same shape as Mom's nursing nipple for the Perfect Fit in baby's mouth, just like Mom, so you know that your baby will love these NUK bottles;1-piece NUK Anti-Colic Air System is built into the nipple to help reduce colic, gas and spit-up. Plus no extra parts to clean.;The Perfect Fit silicone nipples are available in 2 nipple sizes and 3 flow rates. Size 1 is ideal for babies 0 to 6 months and offered in a slow and medium flow. Size 2 is a larger nipple for babies 6+ months and offered in a fast flow.;BPA Free. Dishwasher Safe. Leak-proof nipple sealing hood. For best results when feeding, make sure that the NUK Anti-Colic Air System symbol is under baby's nose so that the unique drinking hole on top side is positioned correctly.;The Perfect Fit silicone nipple features Soft Zone that provides greater comfort for your baby as soft satiny finish conforms to baby's palate.