Abstract: A shaped article is formed of thermoplastic sheeting which consists of a pair of sheets of thermoplastic material spaced apart and interconnected by longitudinally extending ribs. The combination of the sheets and the ribs form elongated passageways in the sheeting. Individual sections of the sheeting have the ends of the passageways sealed closed so that a gaseous medium, such as air, is trapped in the passageways. The sheeting is formed in an extrusion process with one of the sheets having a greater thickness than the other. The individual sections of the sheeting are formed into a shaped article with the sealed character of the passageways being maintained so that the sheets remain in spaced relation in the shaped sections. The difference in thickness between the sheets is selected so that, following the shaping operation, both sheets have substantially the same thickness.