This invention relates to an improvement in a process for producing a composite insulating panel comprised of at least one metal facer having an interior face and an exterior face and a foam core facing the interior face of at least one metal facer and to the resulting composite insulating panel. The improvement in the process for producing the composite insulating panel and improving the fire resistance thereof resides in the steps which comprise: applying an ultrathin intumescent coating composition to the exterior face of said metal facer in an amount to provide a coating thickness of 130 microns or less; and, subsequently providing said foam core facing the interior face of said metal facer.