A material which is composed of two or more materials at a microscopic scale and has chemically distinct phases is called composite material.
Thus, a composite material is heterogeneous at a microscopic scale but statistically homogeneous at macroscopic scale. The materials which form the composite are also called as constituents or constituent materials. The constituent materials of a composite have significantly different properties. Further, it should be noted that the properties of the composite formed may not be obtained from these constituents. However, a combination of two or more materials with significant properties will not suffice to be called as a composite material. In general, the following conditions must be satisfied to be called a composite material:
The combination of materials should result in significant property changes. One can see significant changes when one of the constituent material is in platelet or fibrous form.
The content of the constituents is generally more than 10% (by volume).
In general, property of one constituent is much greater (>5 times) than the corresponding property of the other constituent.
The composite materials can be natural or artificially made materials.