a bathing vessel is made of a sheet of layered materials , which include a first layer of polyurethane material , a second layer of polyurethane material attached to the first layer , a third layer of acrylonitrile butadiene styrene material attached to the second layer , and a fourth layer of acrylic material attached to the third layer . a first narrowed portion about which the sheet bends is provided . the bend defines a first wall and a second wall in the sheet .