40oz Stainless Steel Water Coffee Cup Durable and Long-Lasting Stainless steel is known for its durability and longevity, which is why it's such a popular material for water and coffee cups. A 40oz stainless steel water coffee cup is built to last, even if you drop it or accidentally knock it over. Unlike glass or plastic cups, stainless steel cups won't shatter or crack if they're mishandled, making them a great choice for people who are always on the go.