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They are made from food-grade stainless steel and have a lid that seals in a way to get rid of carbon dioxide. It is made from materials that are BPA free too. The seal also prevents air and moisture from getting into them and so preserving the freshness of the contents. The lid has a clear section to it which means you can see how much is left in the container so you know when to refill it.
You can get this model in 32oz and 64oz sizes and in other colours if you decide you don't want the black.