As a material constant or material constant , a value is a physical quantity called the under predetermined conditions primarily on the used material , however dependent, usually no other external influences. It is therefore a substance's own quantity that assigns a constant value to each substance with regard to a certain substance property . In particular, all molar and specific intensive state variables of pure substances are also material constants at the same time, while their counterparts that are not quantitative or mass-related represent material variables.
However, contrary to their designation, material constants also depend on the size of the sample examined. In the range of a few nanometers, the material properties shift towards the atomic properties. This behavior is called the size effect . An important example of this is the increase in specific resistance in the case of very thin layers.
The density under normal conditions is a material constant , for example, as it is specific to the substance used.