International Copper Research Association sponsored a three-year development program in co-operation with Marston Radiators, Ltd, part of Imperial Metal Industries Ltd (I M I). Their aim was at developing a simplified design that could be manufactured at a much more competitive cost than conventional copper radiators. The outcome has been an assembly, comprising thin brass manifolds of D-section and a copper heat exchange element, the whole of which is pre-assembled and soldered in one furnace heating operation, with a flux that is not corrosive. What little residue this flux leaves is easily flushed away with water.