Membrane keypad is a great input device where you need protection from moist. If you look around you will find that many toys have them. Kitchen, bathroom appliances also may have such buttons. In many areas membrane keypads are replaced by capacitive buttons. Membrane switches are still mechanical device which can wear our or break. If you would like to experiment with membrane switches and probably build something with it, then check out Paul‘s guide on how to build one by yourself.
He used a copper foil tape to make a conductive layers of keypad. He designed keypad and its inner layouts with Adobe illustrator. He stacked a 4×4 keypad and connected it to Arduino to give a test. This is perfect for non intense input devices and you can design your own layout and labeling.