Towers, poles and support structures are used to provide elevation, stabilized support or position control for personnel or equipment. They provide a line of sight for viewing and illumination as well as the transmission and reception of signals. Most towers, poles, and support structure are made of aluminum, steel, stainless steel, wood, plastic or composite materials. Aluminum is a relatively lightweight metallic element that provides high toughness at moderate strength levels. With the addition of copper, aluminum alloys can be heat-treated for higher hardness and greater strength. Carbon and alloy steels offer high toughness and good weldability; however, steel structures need to be painted or coated to prevent rust or corrosion. Stainless steel is highly corrosion resistant, but often too expensive for use in large towers, poles and support structures. Plastic products and fiber reinforced polymers (FRP) provide alternatives to metal materials. Some plastics offer strong dielectric and nonreflective characteristics. Others provide good electrical insulation and are relatively safe for use as mounting brackets or cross arms on power pole lines or towers. Though more costly than traditional plastic materials, fiberglass-reinforced plastic is stronger than wood and easier to maintain. Pressure-treated wood is used mainly for structural or building applications, but is also used for utility poles and lighting applications.