Abstract: A method is provided for producing a polymeric heat exchange panel of the type including a sheet with a multiplicity of longitudinally extending passages and a plurality of juxtaposed dividing walls respectively disposed between adjacent longitudinal passages, wherein each end of the passages is closed to define a manifold space and at least one of an inlet and an outlet communicates with at least one of the manifold spaces. The method includes forming at least one of the manifold spaces by severing longitudinally without substantial removal of dividing wall material said plurality of juxtaposed dividing walls toward and end of the sheet to form severed opposed sides thereof. The method further includes plasticizing the severed opposed sides of the sheet at an elevated temperature and molding the opposed sides together at end edges thereof to form a molded end wall having a longitudinal dimension substantially greater than a thickness of a wall of the sheet.