A heat exchanger having a plurality of heat exchanger plate pairs. Each plate has a longitudinal central planar portion and a peripheral edge portion extending from it. The plate is provided with a first boss and a second boss having an inlet and outlet, respectively. A rib is also provided extending from the peripheral edge portion to the central planar portion, the rib having a mating surface, where the rib mating surface of a first plate in a first plate pair is in contact with a rib mating surface of a second plate in an adjacent plate pair.