What is an electrical insulator and in what forms can it be found?

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Present in all industrial sectors, electrical insulators are indispensable elements, as they serve to protect equipment and people. These insulators come in hundreds of combinations of shapes, materials and assemblies, for sometimes very different applications. Here is a quick overview of these materials.

How to define the electrical insulation capacity of a high performance material?

The function of an electrically insulating material is to prevent the passage of current between two conductive parts subjected to an electrical potential difference. The electrical insulating character of a material is defined by its resistivity, a physical quantity symbolized by the letter ρ (Ω⋅m) and by its dielectric strength, which is the maximum value of the electric field that the material can withstand before an arc is triggered. Thus, a material is said to be insulating when its resistivity is greater than 108 Ω⋅m.

What are the different types of electrical insulators?

Dielectric materials are available in various solid (paper, nonwovens, films) or liquid (resins) forms.

Flexible insulation

Flexible insulations are insulations less than 1 millimeter thick, sold as papers or fibres. For example, papers such as Nomex® are meta-aramids with excellent thermal stability (from -196°C to +300°C). It is therefore the ideal electrical insulator for many applications: transformers, wind turbines, hybrid vehicles, etc. Others, such as Nokamex, a high-end laminate made of Kapton® polyimide and Nomex® aramid paper, have excellent thermal, electrical and mechanical properties.

Rigid laminated insulation

Laminates are a range of insulating materials consisting of several layers of material. Reinforcements (paper, glass mat, glass cloth, mica) constitute the base of the insulation which is coated with phenolic, polyester, epoxy or silicone resin before being polymerized. They can be found in board form, from a few tenths of a millimeter to several dozen millimeters thick. Thus, it is possible to combine the properties of these materials in order to obtain an insulator which presents both high thermal and mechanical electrical performances.

These insulators can be used in motors and transformers, generators, electrical equipment...

Technical films

Films are insulating polymers with a thickness of less than 0.5 mm, available in roll form. Their composition varies enormously and there are many different formulations with their own dielectric, thermal and mechanical properties. Thus, the strong point of Kapton® type polyimides concerns heat resistance (up to 400°C as a short-term thermal peak) with respect to other characteristics which remain very high, whereas Mylar® type polyesters are among the insulators with the highest dielectric values.

Liquid insulators

Electrical insulation can also be provided by using materials in liquid form. This allows the liquid insulation to be placed where it is needed, before curing later. Examples include protective varnishes and mastics. In addition liquid epoxy or polyester impregnating resins can be added to fibre insulation to form rigid composite materials.

Rigid and flexible electrical insulators: examples of applications

The vast majority of industries are concerned with electrical insulation. Insulation is used in the manufacture of motors, cables and transformers, but also in all electronic devices.

Electric motors and generators

In electronics, printed circuit boards are made from a material called FR-4, which is a laminate made from epoxy resin and fibreglass. It is a thick, rigid and fire-resistant material.

Insulators for electronics

Small electric motors operating at low voltages, such as windshield wiper pump motors, can be insulated using flexible polyester insulating films about 100 microns thick because the dielectric character of an insulator varies with its thickness. Flexible insulators are used, for example, in notch back or interphase functions.

On the other hand, on turbo alternator or gas turbine type equipment, we commonly use slot closing materials made of a high performance laminate, thicker, more resistant and combining the advantages of 2 or 3 materials. Example: Nokamex triplex laminates.

Insulators for the automotive industry

In the automotive industry, electrical insulators are found on alternators, cables, and on-board electronics, among others. Moreover, since the arrival of electric and hybrid cars, this need has only increased due to the need to insulate the batteries. For example, Formex®, a polypropylene in film or honeycomb panels, can be used. These solutions can be heat dissipating insulating materials or insulating materials with integrated current conducting properties.


There are many electrical insulation solutions available on the market and their choice depends on the application. Moreover, these materials have varying performances in terms of electrical insulation, temperature resistance and mechanical strength.

Do not hesitate to contact our teams. They will be able to help you choose the right electrical insulation for your needs!

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