Abstract: The pre-fabricated wall assembly comprises essentially a rectangular frame structure provided with first and second panels on opposite sides together with inserts in the form of smaller square-shaped frames of the same depth as the distance between the panels so as to function as reinforcing inserts. Each insert is formed of two long and two short sides, the shorter sides fitting between the ends of the longer sides and being offset so as to provide flow passage therethrough. A polyurethane foam is introduced into the interior of the rectangular frame which foam will flow and fill voids in the inserts as well as all voids between the panels and interior of the frame. The resultant assembly provides a highly heat resistant, soundproof and strong wall assembly for use in construction.