Abstract: A heat exchanger has a plurality of like plates each in turn provided with a base portion substantially on and defining a base plane and having a pair of generally parallel opposite outer edges, and respective lips bent upward from the outer edges and forming and lying on an attachment plane substantially parallel to the base plane. Adhesive bonds or welds secure the plates together in a stack to form generally perpendicular flow passages parallel to the plane. The lips of each plate extend generally perpendicular to the lips of the adjacent plate and the plates are secured together with the connection plane of each plate lying on the base plane of an adjacent plate. Each plate is formed between the respective opposite edges with a plurality of integral bumps projecting from the respective base plane toward the respective connection plane. These bumps each have an apex lying on the respective connection plane.