Compatibility: These bottles are compatible with all Medela breast pumps and the Calma feeding teat, providing seamless integration into your breast pumping routine. This means you can pump, store, and feed using the same container, simplifying the process. Leak-proof Design: The bottles feature screw-on lids to prevent leakage when stored in the fridge, freezer, or during transportation, offering peace of mind for busy parents on the go. Measurement Markings: Clear ounce and millimeter markers on the bottles make it easy to measure the exact amount of milk you've expressed, allowing for accurate portioning and feeding. Convenient Packaging: The 6-pack configuration ensures you have an ample supply of bottles for storing breast milk. This is especially useful for parents who pump frequently or wish to build up a reserve of milk. Complement to Breastfeeding: These bottles are designed to complement your breastfeeding experience, providing a convenient and hygienic way to store expressed breast milk for later use. Overall, the Online Only Medela Breastmilk Collection Storage Bottles offer convenience, compatibility, and reliability, making them an essential accessory for breastfeeding mothers who pump and store breast milk.