If your baby boy doesn't have patient for slow flow, you can switch to the medium flow nipples which releases the milk into your baby's mouth faster. (babygearspecialist.com)
This is most likely due to your let down reflex, which release the milk from where it's stored in your breast and allows it to flow out of your nipples. (lansinoh.com)
The silicone bottles enable parents to squeeze * the bottle gently to release the milk flow. (vitalbaby.com)