Abstract: A set of hinged covers adapted to sealably close the rectangular hatch on the roof of a railway hopper car having a coaming running along the hatch perimeter. Each cover has a vaulted formation to shed water, the long edges of the cover being rolled to define canopies which protectively shield the coaming and a compressible gasket secured to the underside of the cover which presses against the coaming to effect a seal against contaminants. The cover structure is a sandwich laminate of high rigidity and strength constituted by an end grain balsa wood core panel to whose faces are bonded fiberglass skins. The skins are extended beyond the ends of the panel and are interlaminated to define channel-shaped end flanges which cooperate with hinged hold-down bars having an opposed channel formation within which a compressible gasket is nested to seal the ends of the cover.