Refinements in heavy duty piston ring design to suit sealing requirements imposed by different engine designs are presented. Combinations of different individual ring designs used for optimum blowby and oil control in 1968 practice are reviewed. Requirements for piston ring facing materials and parameters for manufacturing processes for application of molybdenum to piston rings are presented. The further development of diesel engines, particularly in the high bmep area, requires further improved piston ring coatings in terms of high mechanical and bond strength, scuff, and wear resistance. The properties of new piston ring facing materials are discussed with particular emphasis on a new multiphase hard plasma-plied material.