Insulators are categorized by installation method into suspension insulators and pole insulators; by the type of insulation material used, they can be porcelain, glass, or composite (also known as synthetic) insulators; by voltage class, into low-voltage and high-voltage insulators; and by environmental conditions, into anti-pollution insulators for dirty areas. Voltage type also gives rise to DC insulators. There are also various special-purpose insulators, such as insulating crossarms, semiconductor glaze insulators, tension insulators for distribution, spool insulators, and wiring insulators, among others. Additionally, they can be divided into two types based on the possibility of insulation breakdown: Type A, non-breakdown insulators, and Type B, breakdown-prone insulators.