It uses a patent - protected two - piece internal vent system for the baby's comfort. (shrewdmommy.com)
In order to prevent these from happening the air vent system makes the air travel from the side of the bottle ring into the bottom of the bottle inside a special tube. (babygearhub.net)
The unique internal green vent system continues to create 100 % vacuum free feeding, which is proven to help reduce wind related colic. (littleangels.ie)