For collection, storage and freezing of breastmilk. Compatible with all Medela breastpumps for pumping directly into the bag. Exclusive self-stick strap attaches directly to breastshield for fast & easy setup. Leak-proof, easy-to-close zipper top. Special plastic retains breastmilk?s beneficial properties. Double-walled for long and safe breastmilk storage. Pre-Sterilized & disposable. 50 per pack.Safe for baby - All parts that come into contact with breastmilk are BPA/DEHP Free.