* Metals. Metals are characterized by their high strength, durability, and electrical conductivity. They are typically hard and solid at room temperature, but can be melted or forged into different shapes. Some common metals include iron, steel, aluminum, and copper.

* Ceramics. Ceramics are inorganic, non-metallic solids that are typically brittle and hard. They are typically made by heating a mixture of clay and other minerals to a high temperature. Some common ceramics include porcelain, pottery, and glass.

* Polymers. Polymers are large molecules that are made up of repeating units called monomers. They are typically soft and flexible, and can be easily molded or shaped. Some common polymers include plastics, rubber, and fibers.

* Composites. Composites are materials that are made by combining two or more different materials to create a new material with properties that are different from the individual materials. Some common composites include fiberglass, carbon fiber, and concrete.