A bathtub, also known simply as a bath or tub, is a container for holding water in which a person or animal may bathe. Most modern bathtubs are made of thermoformed acrylic, porcelain-enameled steel, fiberglass-reinforced polyester, or porcelain-enameled cast iron. A bathtub is usually placed in a bathroom either as a stand-alone fixture or in conjunction with a shower.