Spectra’s Disposable Breast Milk Bags are an easy, convenient, and space-saving way to store your precious breast milk. They are pre-sterilised, so you simply tear them open, pour in the milk, and seal by closing the zipper. As soon as the bag starts filling with milk, the bottom expands so that the bag stands upright by itself in your fridge or freezer. Calibration marks are printed on the bags, as well as a space to fill in the date and time so that you remember to use the oldest milk first. The double-wall designed bags are manufactured of Polyethylene and are BPA-free.