The main property criteria which determine whether a certain material shall be used for a given application are discussed in general terms. The increase in cost of any given material in progressing through the various stages of processing and manufacture is outlined for steel. The general growth trends of production of a range of common metals, cement and plastics in the U.S.A. up to 1960 shows the very high growth rate of aluminium and plastics in recent years compared to other materials. It is shown that by considering the cost per unit of property required that a very useful index is given of the competitiveness of any given material. By way of example, typical costs for one ton of tensile strength given by a range of materials in various forms are tabled.