The bottle works just like the mother's mammary gland. The bottles are equipped with an anti-colic silicone bag that contracts while your baby sucks. No air from outside is required to compensate for the vacuum created in the bottle. Therefore there are no air bubbles, which prevents gaseous colic. Prevents the air from oxidising the milk and destroying the nutrients, especially those in your breast milk. Medium flow teat (M): Allows all types of medium density liquids to flow. Ideal for milk, juices and very low viscosity puree.