A material system composed of a mixture or combination of two or more macroconstituents that differ in form or material composition and are essentially insoluble in each other. This definition is considered to be too broad by some engineers because it includes many materials that are not usually thought of as composites. For example, in many of the particulate-type composites, such as dispersion-hardened alloys and cermets, the composite structure is microscopic rather than macroscopic. Also, this definition does not draw the line between composite materials and composite structures. However, instead of trying to establish a distinction between materials and structures, it is more useful to make a distinction between mill composites (such as nonmetallic laminates, clad metals, and honeycomb) and specialty composites (such as tires, rocket nose cones, and glass-reinforced plastic boats).