The NUK® Seal 'N Go® breast milk storage bags feature a leak-proof zipper that protects against leakage as well as a thicker bag design for ultimate protection. The Seal 'N Go® storage bags are also freezer safe for convenient storage and feature a stand-alone bag design. So easy to use, they can be used with all disposable bottle holders. BPA-free. Package includes 25 pre-sterilized storage bags.