A heat exchanger comprising: a plurality of heat exchange layers (95, 245) stacked in a stackwise direction, each of the layers including a first plate and a second plate, each of the first plate and the second plate including a portion of a first enclosed header (120, 250), a second enclosed header (125, 255) and a plurality of flow channels (130, 260) that extend between the first enclosed header and the second enclosed header, the first plate and the second plate fixedly attached to one another to completely define the first enclosed header, the second enclosed header, and the flow channels; an inlet header in fluid communication in parallel with the first enclosed header of each of the plurality of heat exchange layers to direct a flow of fluid to the heat exchange layers; an outlet header in fluid communication in parallel with the second enclosed header of each of the plurality of heat exchange layers to direct the flow of fluid from the heat exchange layers; characterized in that it further comprises a plurality of fins, each positioned between adjacent heat exchange layers; in that the inlet header includes an outer wall, an inner wall, and a filler plug that defines a longitudinal axis, and wherein the inner wall and the filler plug cooperate to define an inner space that receives the flow of fluid from a source, and the inner wall and the outer wall cooperate to define an outer space that directs the flow of fluid to each of the heat exchange layers; and in that the inner wall includes a plurality of ribs that cooperate with the outer wall to divide the outer space into a plurality of separate annular spaces. a plurality of heat exchange layers (95, 245) stacked in a stackwise direction, each of the layers including a first plate and a second plate, each of the first plate and the second plate including a portion of a first enclosed header (120, 250), a second enclosed header (125, 255) and a plurality of flow channels (130, 260) that extend between the first enclosed header and the second enclosed header, the first plate and the second plate fixedly attached to one another to completely define the first enclosed header, the second enclosed header, and the flow channels; an inlet header in fluid communication in parallel with the first enclosed header of each of the plurality of heat exchange layers to direct a flow of fluid to the heat exchange layers; an outlet header in fluid communication in parallel with the second enclosed header of each of the plurality of heat exchange layers to direct the flow of fluid from the heat exchange layers; characterized in that it further comprises a plurality of fins, each positioned between adjacent heat exchange layers; in that the inlet header includes an outer wall, an inner wall, and a filler plug that defines a longitudinal axis, and wherein the inner wall and the filler plug cooperate to define an inner space that receives the flow of fluid from a source, and the inner wall and the outer wall cooperate to define an outer space that directs the flow of fluid to each of the heat exchange layers; and in that the inner wall includes a plurality of ribs that cooperate with the outer wall to divide the outer space into a plurality of separate annular spaces.