You don't have to replace the entire bottle, just buy bags that will easily fit the bottle.

The set includes two pieces of silicone bags in the size of 270 ml.

This patented silicone bag is stretched during feeding depending on how the baby sucks, similarly to what happens in the mammary glands of a breastfeeding woman. This innovative system causes the lack of air bubbles in the food, so the baby does not swallow air that could cause colic. This system also prevents milk from oxidizing and losing important nutrients.