A heat exchanger having a manifold defined by a plurality of connected closure pieces. A corner of the manifold is defined by the connected joint of three closure pieces, where one closure piece has a bent edge abutting an end of a second closure piece adjacent a generally flat section of a third closure piece. The bent edge of the one closure piece adjacent the manifold corner is a bend in a thin portion of the one closure piece, where the thin portion has a sheet thickness which is less than the sheet thickness of the adjacent portions of the one closure piece. Multiple corners of the manifold can be formed in this manner by thinning the thin and bending the portion, then connecting the closure pieces using solder to form a seal in the open cross section at the corners.