Composite materials are usually classified by the type of reinforcement they use. This reinforcement is embedded into a matrix that holds it together. The reinforcement is used to strengthen the composite. For example, in a mud brick, the matrix is the mud and the reinforcement is the straw. Common composite types include random-fiber or short-fiber reinforcement, continuous-fiber or long-fiber reinforcement, particulate reinforcement, flake reinforcement, and filler reinforcement.
One type of very old composite material invented by early humans was the mud brick. A normal mud brick is sturdy and resistant to compression, but can break if bent. Straw is a material that has excellent tensile strength, meaning that it resists stretching. By combining both, early humans were able to create composite mud bricks that could resist weight and compression as well as stretching.
Concrete is a composite material made of cement, sand, stones and water. Combined, concrete is stronger than any one of these materials. Concrete is used heavily in building and road construction.
Fiberglass is a material made of tiny glass shards held together by resin and other components. In the automotive industry, fiberglass is important for making body kits. The body shell for a car is made up of different layers of fiberglass, such as a gel-coat layer, tissue layer, matting and cloth. The final product is a complete, waterproof, lightweight and strong body kit. Fiberglass can also be a less expensive alternative to other materials.
Composites can be easily found in nature. Wood is an example of a composite because cellulose fibers are held together by substance called lignin. These fibers can be found in cotton and thread, but it's the bonding power of lignin in wood that makes it much tougher. Another natural composite is rock and sand, materials used in concrete. Rock is just smaller rocks held together, and sand is made of small grains.