This essential cooler is a mom favorite as a feature of Medela double electric breastpumps. It's compatible with X4 Medela 5oz breastmilk bottles to keep breastmilk cool on the go. Great as an extra for transporting breastmilk. All Medela breastmilk bottles and products that come in contact with breastmilk are and always have been made without BPA.Authentic Medela Spare Parts are engineered, tested and approved to work specifically with your Medela breastpump. Non Medela spare parts can vary significantly in design, materials, and workmanship; all of which may affect the performance of your Medela breastpump.