Composite materials are formed by combiing two or more materials that have quite different properties. The different materials work together to give the composite unique properties, but within the composite you can easily tell the the different materials apart – they do not dissolve or blend into each other. Modern aviation, both military and civil, is a prime example. It would be much less efficient without composites. In fact, the demands made by that industry for materials that are both light and strong has been the main force driving the development of composites. The greatest advantage of composite materials is strength and stiffness combined with lightness. By choosing an appropriate combination of reinforcement and matrix material, manufacturers can produce properties that exactly fit the requirements for a particular structure for a particular purpose. In general, composite materials are very durable. The downside of composites is usually the cost. Although manufacturing processes are often more efficient when composites are used, the raw materials like steel, but in many cases they are just what we need.