Types of Electrical Insulation: Materials, Properties & Applications

In electrical applications, every component plays a role in system performance and safety, including the types of electrical insulation used to protect wires and components. Electrical insulation provides essential protection, such as preventing current leakage and electrical shorts and protecting against heat, moisture, chemicals, and mechanical damage. 

Understanding the different types and their properties helps ensure the right solution for an application, and this guide explains the different electrical insulation types across the two primary categories.

• Explanation of thermoplastic vs thermoset.
• Common types and characteristics of electrical insulation materials.
• Examples of applications for different types of electrical insulation.
• How to choose the right type for applications.

Wire or cable insulation can be composed of various plastics or polymers, with the two most commonly used types being thermoplastic and thermoset. 

Thermoplastic insulation has a low melting point, allowing it to soften and melt when heated. Once shaped, the material solidifies when cooled. The ability to heat, reshape, and cool without degrading the material makes thermoplastic highly reusable. However, this ability also makes this electrical cable insulation material sensitive to heat. Although thermosplastics are more sensitive to heat, they offer excellent resistance to corrosion, industrial chemicals, and mechanical impacts. They are also relatively inexpensive to produce, offering better affordability.

Thermoset wire insulation can also change shape when heated. However, unlike thermoplastics, this material undergoes a permanent chemical change during processing. Known as curing, it prevents the material from softening or reshaping when reheated. Thermosets are strong, flexible, and more stable under extreme temperatures than thermoplastics, especially at low temperatures. However, extreme overheating can degrade the material. These types of electrical insulation offer superior resistance to oils, UV rays, moisture, and harsh industrial chemicals.

Electrical wire insulation keeps current contained and flowing through the wire, helping prevent electric shocks and short circuits when wires touch. Insulation also protects the conductive metal core from damaging moisture, heat, and corrosion. An understanding of the different types of electrical insulation, their characteristics, and common applications helps when specifying the best fit for an application.

PVC is a thermoplastic and one of the most widely used and versatile materials for electrical wire and cable insulation, including heat shrink tubing. It’s relatively easy to process and is generally one of the more economical insulation materials available. Its flame, moisture, abrasion, and chemical resistance properties make it suitable for a broad range of applications. PVC is available in standard, semi-rigid, and irradiated formulations. Generally, the recommended operating temperatures range from approximately -55°C to 105°C.

PVC's high attenuation and capacitance loss, however, may affect performance. It’s also not ideal for environments requiring high flexibility and extended flex life at low temperatures.

Polyethylene (PE) is an excellent electrical cable insulation material, offering a low dielectric constant, stable dielectric performance across a broad frequency range, and very high insulation resistance. These electrical properties help minimize signal attenuation, making it a good choice for coaxial and high-frequency communication cables. As a thermoset insulation, polyethylene offers little flexibility and performs well at operating temperatures ranging from -65° Celsius to +80° Celsius. However, it is flammable. Although additives can help make it more flame-retardant, they can also impair the dielectric constant and increase power loss. 

Compared to standard PE, Cross-Linked Polyethylene (XLPE or XLP) offers high dielectric strength, low dielectric loss, and a relatively low dielectric constant. Its cross-linked structure provides greater thermal stability and durability. With a typical continuous operating temperature of up to 90°C, it works well in applications exposed to higher operating temperatures. It also has a high resistance to moisture and environmental stress often found in demanding environments such as industrial and aerospace settings.

Silicone is recognized for excellent high and low-temperature performance and flexibility. It can generally withstand continuous operating temperatures ranging from approximately −60°C to 200°C. Silicone also offers very good resistance to moisture, weathering, and many environmental conditions, as well as high dielectric strength, insulation resistance, and chemical resistance. This thermoset elastomer is commonly used in high-temperature applications, such as heating equipment, lighting, industrial machinery, and aerospace.

Drawbacks of silicone include a relatively higher cost than PVC and PE, and lower resistance to abrasion and mechanical damage. Therefore, it can be less suitable for applications where the insulation will experience significant physical wear.

Fluoropolymer electrical wire insulation types include:

• Polytetrafluoroethylene (PTFE)
• Fluorinated Ethylene Propylene (FEP)
• Ethylene Tetrafluoroethylene (ETFE)
• Irradiated Ethylene Tetrafluoroethylene (Cross-Linked ETFE)
• Perfluoroalkoxy (PFA)

Fluoropolymers are a specialized family of high-performance synthetic plastics that contain strong carbon-fluorine bonds. These electrical insulation types offer exceptional resistance to extreme temperatures, chemicals, moisture, and environmental degradation. Fluoropolymers also have remarkable electrical insulation properties, making them well suited for demanding aerospace, military, and industrial applications.

Ethylene propylene rubber (EPR) offers outstanding temperature resistance, with an operating temperature range of -50C to 150C. As a thermoset elastomer, it offers excellent dielectric strength and temperature resistance. This type of insulation resists heat, weathering, oxidation, alcohol, water, acid, alkali, and other organic solvents. EPR is commonly used for medium voltage power cable insulation because it can withstand moisture, temperature fluctuations, mechanical movement, and other demanding environmental conditions. Although it has excellent resistance to cracking and aging, it is not as tear-resistant as other types of electrical insulation.

Thermoplastic rubber combines rubber-like flexibility with the processing characteristics of a thermoplastic. It can withstand repeated bending and movement while remaining relatively easy to manufacture through extrusion. TPR offers a continuous operating temperature range of approximately −40°C to 105°C, but some formulations can operate outside this range. It has excellent flexibility, good electrical insulation, abrasion resistance, and durability. It’s well-suited for applications requiring repeated bending or movement, like industrial, control, and instrumentation cables.

There isn’t a universal wire insulation material that's ideal for every application. The application's requirements and operating environment will help determine which insulation material is best suited to the job. For example, as discussed in our wire splice guide, electrical characteristics such as voltage and frequency can influence insulation requirements. To get an idea of how the different types of electrical insulation materials apply in different applications and industries, here’s a quick comparison table. Although each of these is commonly used for the listed applications, it’s important to note that the appropriate material will ultimately depend on the specific requirements of each application.

Choosing among the different types of electrical insulation to find the best fit begins with the application, as the insulation material's properties must align with the application. If you already know which standards or regulatory requirements apply (UL, CSA, CE, SAE, ISO), many of your questions are already answered.  

If not, key questions to ask include:

• What are the operating temperature requirements?
• What are the dielectric strength and voltage requirements?
• What is the environmental exposure, including UV, moisture, or chemicals?
• Is there any required mechanical flexibility?

Using an inappropriate wire insulation in your application or wire harness design affects performance, reliability, safety, and compliance. 

Selecting the right components and solutions for any application is critical. Failure of a single component can jeopardize an entire system, disrupting operations and creating costly delays. That’s why it’s important to source components from a reputable distributor like Peerless Electronics. As an authorized distributor for leading electronic component manufacturers, Peerless provides quality products backed by 24/7 technical support, extensive Value-Added Services, and a quality management system certified to AS9100D and ISO 9001:2015 (view official certificate PDF).