Abstract: An improved extrusion design is disclosed for use in constructing insulated windows, curtain walls and the like which incorporate a thermal barrier insulator between inner and outer portions of their structure. The extrusion includes a channel defined by mutually opposing surfaces of the inner and the outer portions together with a temporary bridging section which is later removed after the channel is filled with the thermal barrier insulator. The extrusion includes a reinforcing section which is connected solely to the bridging section and extends transversely across the channel. The channel may be filled with the insulating material such that it surrounds the reinforcing section and is mechanically interlocked therewith to increase its strength. When the bridging section is removed, the reinforcing section is completely isolated from the inner and outer portions of the extrusion so as not to degrade the thermal insulating properties of the structure.