The invention relates to a plate-type heat exchanger having a plate block comprising partition plates which delimit flow channel layers between the plates. According to the invention, the partition plates have a solid or folded edge, which projects out of the plane of at least one main side of the partition plates at the edge side, along closed-edge regions which are spaced apart from one another in the peripheral direction by means of intervening open-edge regions. In the plate block, this solid or folded edge is joined in a fluid-tight manner to the opposite edge region of an adjoining partition plate and functions as a lateral boundary for the associated flow channel layer. Such heat exchangers may be used, for example, in automobiles and reactors of fuel cell systems.