The Natural Response nipples behave more like a breast so your baby can drink, swallow milk, and breathe using their natural rhythm and drinking style. Milk only flows from the nipple when your baby actively drinks. Babies who are used to free-flow bottles will need to adapt to the new drinking style and will need some time to switch to the Natural Response nipple.
Most babies are sensitive to change, so adjusting to a new way of feeding may take a few attempts. When introducing a new bottle to your little one, feed them when they are relaxed and not hungry. If you have attempted to feed a few times with no success, it could be a sign that your baby needs a different nipple with another flow rate.