The toughness, processing temperature and processing characteristics of unplasticized PVC compounds can be improved by adding polymeric modifiers. Using a number of examples to illustrate this, the author discusses formulations and properties of such compounds which are distinguished by, among other things, their transparency and good heat resistance. Polymeric modifying additives discussed in the paper include ABS; methyl methacrylate/butadiene/styrene copolymers; ethylene/vinyl acetate/vinyl chloride copolymers; chlorinated PE.