Wire insulation does much more than keep a conductor covered. The right insulation helps a wire harness withstand heat, moisture, chemicals, vibration, abrasion and repeated movement.

For a custom wire harness, choosing the insulation material should depend on the actual working environment rather than price alone.

What Is Wire Insulation?

Wire insulation is the non-conductive material surrounding an electrical conductor.

Its primary job is to prevent unwanted electrical contact between conductors and surrounding components. At the same time, it protects the conductor against environmental and mechanical damage.

In a wire harness, insulation can affect:

• Operating temperature

• Flexibility

• Abrasion resistance

• Chemical resistance

• Moisture resistance

• Cable diameter

• Weight

• Flame performance

• Service life

The properties vary significantly between different polymer formulations, so there is no single insulation material that is suitable for every application. PVC, polyethylene, cross-linked polymers, fluoropolymers, TPE and silicone are all used in modern wire and cable constructions.

Wire Insulation vs. Cable Jacket

These two terms are sometimes confused.

Insulation directly surrounds an individual conductor and provides electrical isolation.

A jacket normally surrounds several insulated conductors or the complete cable and provides additional mechanical and environmental protection.

For example, a multi-conductor cable may use PVC insulation around each conductor and then add an outer PVC or polyurethane jacket around the entire cable.

When selecting a custom cable assembly, both layers may need to be considered.

1. PVC Insulation

Polyvinyl chloride, or PVC, is one of the most widely used wire insulation materials.

It offers a practical balance between cost, flexibility, electrical performance and general environmental resistance. Different PVC compounds can also be formulated for flame resistance, oil resistance and different temperature requirements.

PVC is commonly found in:

• Consumer electronics

• Home appliances

• Control equipment

• Internal equipment wiring

• General-purpose wire harnesses

• Automotive circuits with moderate environmental requirements

Advantages of PVC

PVC is economical and easy to process. It is available in many colors and works well for applications where extreme temperature or chemical exposure is not a major concern.

Limitations of PVC

Its temperature and chemical performance depend heavily on the formulation. Standard PVC may not be the best choice near very hot components or in environments with aggressive chemicals.

For these applications, XLPE, silicone or fluoropolymer insulation may provide better long-term performance.

2. XLPE Insulation

XLPE, or cross-linked polyethylene, is polyethylene that has been modified through cross-linking.

Cross-linking improves the material's thermal stability and allows it to maintain its physical properties at higher temperatures than conventional polyethylene. Some XLPE constructions are designed for operating temperatures around 125°C, although the exact rating must always be confirmed from the wire specification.

XLPE is commonly used in:

• Automotive wiring

• Engine compartments

• Industrial equipment

• Battery systems

• Power distribution

• Heavy-duty vehicles

Why XLPE Is Popular in Automotive Harnesses

Automotive cables must deal with heat, vibration, fluids and tight installation spaces.

Cross-linked insulation provides a useful combination of heat resistance, durability and relatively thin insulation walls.

Automotive wire names such as GXL, TXL and SXL are commonly associated with cross-linked insulation constructions, although the exact specification should always be confirmed according to the applicable automotive standard.

Modern automotive cable requirements are covered by standards such as the ISO 19642 series, which includes test methods for electrical cables used in road vehicles. ISO 19642-2:2023 replaced earlier test-method standards including parts of ISO 6722.

3. Silicone Wire Insulation

Silicone is a good choice when a harness needs both high-temperature resistance and excellent flexibility.

Unlike some harder plastics, silicone remains soft and flexible across a wide temperature range. Commercial silicone hook-up wires are available with ratings reaching 150°C or 200°C depending on their construction.

Typical applications include:

• Heating equipment

• Battery systems

• LED lighting

• Medical equipment

• Sensors

• High-temperature appliances

• Industrial machinery

Advantages of Silicone

Its flexibility makes silicone especially useful where wires must bend around components or remain flexible in cold environments.

Limitations of Silicone

Silicone insulation can be softer than some thermoplastic or fluoropolymer materials. If the wire will repeatedly rub against sharp metal surfaces, additional sleeving or mechanical protection may be necessary.

4. Fluoropolymer Insulation: PTFE, FEP and ETFE

Fluoropolymer insulation is used when normal wire materials cannot provide enough resistance to temperature, chemicals or harsh environments.

The most common options include:

PTFE – Polytetrafluoroethylene
FEP – Fluorinated ethylene propylene
ETFE – Ethylene tetrafluoroethylene

These materials are not identical.

PTFE is well known for very high-temperature capability. FEP combines high-temperature performance with easier processing, while ETFE is frequently selected where mechanical strength, chemical resistance and thin-wall construction are important.

TE Connectivity, for example, uses modified cross-linked ETFE in high-performance wire constructions and highlights its thermal, mechanical and environmental properties.

Typical Applications

Fluoropolymer-insulated wires can be found in:

• Aerospace equipment

• High-temperature sensors

• Medical devices

• Industrial systems

• Automotive electronics

• Test equipment

• Compact electronic assemblies

Advantages

The main advantages are high temperature resistance, good chemical resistance and the ability to provide strong performance with relatively thin insulation in suitable constructions.

Limitations

Cost is usually higher than PVC or conventional polyethylene-based insulation. Using fluoropolymer wire in a simple room-temperature application may therefore increase harness cost without providing a meaningful benefit.

5. TPE and TPR Insulation

TPE, or thermoplastic elastomer, combines some rubber-like characteristics with thermoplastic processing.

It is useful when the cable must remain flexible and tolerate repeated movement.

Depending on the formulation, TPE materials can provide resistance to oils, fuels, solvents and water while maintaining flexibility at low temperatures.

Common applications include:

• Moving machinery

• Robotics

• Portable equipment

• Industrial control systems

• Appliances

• Flexible cable assemblies

TPE is particularly useful when flexibility is a more important design factor than simply achieving the lowest material cost.

6. PE and PP Insulation

Polyethylene (PE) and polypropylene (PP) are also widely used in electrical cable constructions.

PE offers useful electrical properties and resistance to moisture and many chemicals. Its dielectric characteristics make it particularly useful in signal transmission and communication cable applications.

PE and PP can be found in:

• Communication cables

• Signal cables

• Coaxial cables

• RF applications

• Electronic equipment

• Multi-conductor cables

For a wire harness carrying sensitive signals rather than only DC power, the electrical properties of the insulation can become an important part of the cable design.

Quick Comparison of Common Wire Insulation Materials

Important: These are general comparisons rather than universal ratings. Temperature, voltage, wall thickness, flame performance and chemical resistance vary by individual wire construction and specification.

How to Choose the Right Wire Insulation

Choosing wire insulation should start with the application rather than the material name.

Before specifying a wire for a harness, consider the following factors.

Operating Temperature

Determine both the normal operating temperature and possible short-term temperature peaks.

A control cable installed inside room-temperature equipment has very different requirements from a cable routed near a motor, heater or automotive engine.

Do not automatically choose the highest temperature rating. Higher-performance materials normally increase cost.

Voltage Requirements

Insulation must be suitable for the system voltage and the applicable safety requirements.

However, insulation material alone does not determine a wire's voltage rating. Wall thickness, construction and certification also matter.

Always evaluate the complete wire specification.

Flexibility and Movement

A stationary wire inside an enclosure and a cable moving continuously inside a robotic arm should not necessarily use the same construction.

For dynamic applications, consider conductor stranding, insulation flexibility, bend radius and expected movement cycles together.

Oil and Chemical Exposure

Automotive, industrial and manufacturing equipment may expose wiring to oil, fuel, coolant, cleaning chemicals or solvents.

In these environments, material compatibility should be confirmed before production. High-performance automotive and industrial wires are often designed specifically around fluid resistance requirements.

Abrasion and Mechanical Protection

A cable routed through a protected plastic enclosure requires less abrasion resistance than a harness mounted near moving metal parts.

If abrasion cannot be avoided, the solution may involve both a more durable wire material and additional protection such as:

• Braided sleeving

• Corrugated tubing

• Heat-shrink tubing

• Protective conduit

Heat-shrink products are commonly used to add electrical insulation, mechanical protection, environmental sealing and strain relief around harness components.

Installation Space

Thin-wall wire can reduce harness diameter and make routing easier in compact products.

This can be important in automotive electronics, medical equipment, sensors and densely packed electronic devices.

The smallest cable, however, is not automatically the best cable. Mechanical strength and production requirements still need to be considered.

Is More Expensive Insulation Always Better?

No.

A common mistake in custom wire harness design is selecting the most technically advanced material instead of the material that actually matches the application.

For example, PTFE or ETFE may offer excellent performance, but a standard indoor electronics harness may work perfectly with PVC at a much lower cost.

On the other hand, reducing cost by using basic PVC in a high-temperature or chemically aggressive environment can result in premature insulation failure.

The goal is not to select the cheapest or most expensive wire.

The goal is to select the right wire for the actual operating conditions.

Choosing Wire Insulation for a Custom Wire Harness

When requesting a custom wire harness, providing only the connector model and cable length is often not enough.

For more accurate material selection, provide your supplier with:

• Working voltage

• Current

• Wire gauge

• Normal operating temperature

• Maximum temperature

• Indoor or outdoor use

• Chemical exposure

• Waterproof requirements

• Flexing or movement requirements

• Required certifications

• Connector and terminal specifications

• Drawing or wiring diagram

With this information, the wire material can be selected together with the connector, terminal, conductor size, protective sleeving and harness structure.

RY manufactures custom wire harnesses and cable assemblies according to customer drawings, samples and application requirements, including products using different conductor and insulation constructions.

Conclusion

Wire insulation directly affects how reliably a cable assembly performs in its real operating environment.

PVC is practical for many general applications. XLPE works well where higher heat and environmental resistance are required. Silicone provides excellent flexibility at elevated temperatures, while fluoropolymers such as ETFE, FEP and PTFE are better suited to demanding chemical and high-temperature environments.

Instead of choosing an insulation material by name alone, consider temperature, voltage, movement, chemicals, abrasion, installation space and applicable standards together.

If you are developing a custom wire harness, send us your drawing, connector information, wire specifications and application requirements. We can help you evaluate a suitable cable construction for your project.

Frequently Asked Questions

Does wire color affect insulation performance?

Usually no. Color is primarily used for circuit identification, assembly control and maintenance. However, special pigments or application requirements can affect the available material choices, so custom colors should still be confirmed with the wire supplier.

Can different insulation materials be used in the same wire harness?

Yes. One harness may contain several types of wire. For example, high-temperature wires may be used near a heater while standard wires are used in cooler areas of the same assembly.

Why does insulation thickness matter when choosing a connector?

The outside diameter of the insulated wire affects terminal crimping, connector seals, wire routing and cavity compatibility. Two wires with the same AWG conductor can have different overall diameters because their insulation constructions are different.

Should outdoor wire harnesses always use waterproof wire?

Not necessarily. Waterproof performance depends on the complete harness design, including connectors, seals, splices, overmolding and cable entry points. Insulation material is only one part of the waterproofing system.

Can an existing wire harness be changed to a different insulation material?

Yes, but the replacement should be reviewed carefully. A different material may change wire diameter, flexibility, stripping parameters, crimp settings and connector seal compatibility. Sample validation is recommended before mass production.