A novel insulated wall structure is formed with upright hollow thermoplastic extrusions connected together in a row, with the extrusions presenting a row of compartments (15,22,30) adapted to receive concrete (39) extending along the length of the wall structure and a row of compartments (16,23,33) containing or adapted to receive insulation (38) material also extending along the length of the wall along side or in parallel with the row of concrete receiving compartments (15,22,30) whereby when the compartments (15,22,30) adapted to receive concrete (39) are filled with concrete (39) and the insulation (38) receiving compartments (16,23,33) are filled with insulation (38) the insulation (38) in said insulation (38) receiving compartments (16,23,33) is positioned to block heat transfer through the wall. Also novel wall forming units or components for the wall structure in the form of elongated hollow thermoplastic extrusions having internal walls (12,13,14,21,29,32) to provide the requisite concrete (39) receiving and insulation (38) receiving or containing compartments (15,16,22,23,30,33).