The manufacture and successful functioning of a product, be it large or small, involves an essential, and often complex, design sequence. This sequence contains many interacting factors including the performance requirements of the product, its size and shape; the number of articles to be made, and then the method of production; the cost, and the choice of the material from which the article is to be made.Considering these factors, it is obvious that on purely the criterion of properties, any one of a number of different materials could be used for most applications. Whilst the final choice of materials is almost invariably made on price, there are certain exceptions where either technology has advanced to such a stage that a reversal away from plastics materials would be detrimental, or where design criteria make plastics the only choice. Cost comparisons can and should be made at several stages in the overall production route; in terms of basic raw materials costs, conversion or fabrication costs, and the finishing operations.Note This paper was received at the Institution in October 1974.