A range of films of mixed composition, prepared by arc plasma spraying, has been investigated. Both free powder and powder in a plastic binder forming a rod have been used in the spray process. A variety of mixtures of insulators, metals and semiconductors has been examined and it is shown that resistivity/temperature curves for the specimens produced have in general two points of inflection, the temperatures of which vary with composition. This allows prediction of a composition giving low T.C.R. at room temperatures for any given metal/semiconductor combination. A qualitative theoretical model explaining this effect is presented. It has also been demonstrated that a conductor/insulator combination need not necessarily exhibit a sharp transition. This allows a broad range of resistance values to be obtained simply by varying composition.