Abstract: A multilayer heat exchanger device comprises: a stack of double sided plates arranged to provide multiple fluid flow paths separated by the plates; wherein the double sided plates each have an array of heat exchanger fins extending outward from both sides of a body of the plate into the fluid flow paths on either side of the plate; and wherein outer ends of the fins of the double sided plates are bonded on each side of the plates to the fins, or between the fins, of the adjacent plates. The double sided plates may be manufactured by etching.