These are our strongest bags yet! NUK Seal ‘n Go Breast Milk Storage Bags safely and securely store precious breast milk in either the refrigerator or freezer until you are ready to feed your baby. Designed for collecting, storing, and freezing breast milk, these bags are 100% leak-proof with double zipper seals. They are also freezer safe and self-standing, so easily sit or lay flat on your freezer shelf until ready for use. The oxygen barrier permits breast milk to stay fresh during storage.