Abstract: Common problems with composite panels of the foam core and metal facing type include water infiltration, failure to survive fire testing, and fragility. A relatively simple panel which affords a solution to the above mentioned problems includes a foam core with inner and outer metal facings thereon, a pair of spaced apart projections extending longitudinally of one side of the core defining male connectors, a pair of longitudinally extending, spaced apart grooves in the other side of the core defining female connectors for receiving the projections, the inner and outer facings terminating in the areas between the connectors so that there is core to core and metal to metal contact when panels are interconnected, a recess in an outer corner of the male connector side of the core, and a flange on the other side of the panel, whereby, when panels are interconnected side edge to side edge, the flange overlaps the recess leaving an expansion gap for fasteners, which are covered by the flange.