A hard cover for spas, hot tubs and the like has an outer layer defining one or more cover portions that may be hinged together along a common top edge. Each cover portion internally includes a plurality of rigid panels, which may be made of expanded polystyrene or another rigid foam or the like. A support structure that mechanically couples and/or supports the panels is provided to improve the load-bearing capacity of the spa cover, optionally providing sufficient strength to conform to applicable safety standards. The support structure can include beams having various cross-sections, or combinations thereof, and may be provided in multiple segments that are shorter than the overall length of the cover. A vapor barrier film can be provided that encloses the panels and optionally some or all portions of the support structure to protect these components from degradation in the spa environment.