You can change the nipple portion to different flow rates as your baby grows and gets better at bottle feeding. (abckidsinc.com)
If your baby hasn't been so keen on the bottle thus far, you might want to try different bottles and nipples with different flows until you find the right fit. (whattoexpect.com)
Most companies produce nipples in three or even four different flow rates, make sure you pick a correct one for your baby's needs. (babygearhub.net)