The NUK Breast Milk Bags are not only easy to fill, they are also produced hygienically, making them ready for immediate use, so that the breast milk can be frozen quickly, simply and safely. They are flexible and can be stacked on top of each other when stored in fridges and freezers. Our tip: milk freezes faster when laid flat than when upright. So, always place the NUK Breast Milk Bags horizontally to freeze. The double safety fastening keeps the precious milk inside the leakproof bag, which is made of stable, freeze-safe, BPA-free plastic. Thanks to its heat-sealed seams, it cannot tear or burst. Includes a practical pouring spout s no more spills when filling the milk into the bottles.