Composite materials often consist of substrates or base materials manufactured using a paper making process. Many types of organic fibers can be made into a paper substrate. An example of an organic fiber would be cellulose produced from trees. Another example would be the synthetic aramid fiber pioneered by DuPont and marketed as Nomex. Other naturally occurring materials such as mica can also be made into a paper substrate. These papers can be manufactured into insulating materials individually or can be combined with other materials to form a composite insulation material commonly called a flexible laminate.

Insulating films such as polyester film are also used in a wide range of electrical insulation applications. Though films do not typically have very good mechanical or thermal properties, they do offer excellent dielectric characteristics. Thus, polyester films are used in combination with insulating papers such as rag paper or Nomex paper in order to form a composite with an excellent combination of mechanical, thermal, and electrical properties.

Insulating papers are most commonly used in applications where a thin layer of insulation is required. These applications typically require the material to be bent, formed, or simply punched into a shape that fits into a confined space. Typically applications include layer insulation in transformer coils, slot insulation in motors, turn-to-turn insulation in power generators, and phase-to-phase insulation in low voltage circuit breakers.

Because insulating papers maintain their dimensional stability at elevated temperatures, these materials have been used in electrical insulating applications since their discovery. Electrical equipment tends to generate a tremendous amount of heat due to the concentration of electrons moving in a small space. The passage of electricity through electrical wires creates thermal energy or heat due to the resistance offered by copper or aluminum to the passage of electrons through their valence structures. Thus, the materials that insulate the copper or aluminum conductors must be able to withstand the thermal energy created without deforming or melting. In fact, most high voltage transmission cables are wrapped with insulating paper.

Examples of insulating papers include:

More information

• Insulating Material Technical Data Sheets