An insulated fire door includes a door shell having spaced first and second exterior panels and a gypsum panel between the first and second exterior panels. The insulated fire door includes a plurality of spacers bonded across an interior side of each of the first and second exterior panels. The spacers maintain the gypsum panel in a spaced position from the interior sides of the first and second exterior panels as the door bows during a fire on one side of the door, until the gypsum disintegrates. Each of the spacers may have a flat portion contacting the gypsum panel, a leg extending from the flat portion spacing the gypsum from the interior sides of the first and second exterior panels, and a flange extending from the leg bonding the spacer to the first and second exterior panels.