The materials used in a wire harness determine its electrical performance, durability, weight, and cost. Selecting the right combination of conductor, insulation, shielding, and outer protection materials is essential for ensuring the harness performs reliably in its intended environment.
This guide covers the major material categories used in wire harness construction, with comparison tables and guidance for matching materials to application requirements.
Wire Conductor Types
The conductor is the core of every wire, carrying electrical current from source to load. Conductor selection affects current capacity, flexibility, weight, and cost.
Solid vs Stranded Conductors
Solid conductors consist of a single metal wire. They are less expensive, easier to terminate in screw-type terminals, and have slightly lower DC resistance than equivalent stranded wires. However, solid conductors are rigid and will break if subjected to repeated flexing. They are used in fixed installations such as building wiring and control panel connections.
Stranded conductors consist of multiple thin wires twisted together. They are flexible, resistant to vibration fatigue, and easier to route through complex harness paths. Stranded conductors are standard in nearly all wire harness applications. Strand count and individual strand diameter determine flexibility — more strands of finer wire produce a more flexible conductor. Fine-stranded and extra-fine-stranded wires are used where maximum flexibility is required, such as robotic arms and moving door harnesses.
Conductor Materials
Bare Copper (BC): The standard conductor material for wire harnesses. Bare copper offers excellent electrical conductivity (second only to silver among practical metals), good ductility, and reliable crimp and solder termination. It is the default choice for most applications.
Tinned Copper (TC): Copper wire coated with a thin layer of tin. Tinning protects against oxidation and corrosion, improves solderability, and extends shelf life. Tinned copper is preferred for marine environments, harsh industrial settings, and applications requiring long-term storage before assembly.
Copper-Clad Aluminum (CCA): An aluminum core with a copper outer layer. CCA is approximately 60% lighter than solid copper and less expensive, but has higher resistance (about 65% of copper’s conductivity) and can be more difficult to terminate reliably. CCA is used where weight and cost reduction are priorities, such as in some automotive and consumer electronics applications, but it is not accepted in all industry standards.
Aluminum: Used primarily in high-voltage power distribution and some automotive battery cables where weight savings are significant. Aluminum has about 61% of copper’s conductivity, requiring larger cross-sections for equivalent current capacity. Special terminals and crimping techniques are needed to prevent galvanic corrosion at aluminum-copper junctions.
Insulation Materials Comparison
Wire insulation is the protective layer surrounding the conductor. The insulation material determines the wire’s temperature rating, flexibility, chemical resistance, and flammability characteristics. The following table compares the five most common insulation materials used in wire harnesses.
| Property | PVC | XLPE | PTFE (Teflon) | Silicone | FEP |
|---|---|---|---|---|---|
| Temperature Range | -40°C to +105°C | -40°C to +125°C | -200°C to +260°C | -60°C to +200°C | -200°C to +200°C |
| Flexibility | Good | Moderate | Low (stiff) | Excellent | Good |
| Chemical Resistance | Moderate | Good | Excellent | Good | Excellent |
| Abrasion Resistance | Moderate | Good | Good | Poor | Good |
| Flame Resistance | Self-extinguishing (with additives) | Good | Excellent (non-flammable) | Self-extinguishing | Excellent |
| Relative Cost | Low | Low-Medium | High | Medium-High | High |
| Typical Applications | General wiring, appliances, automotive interior | Power cables, underground, solar | Aerospace, military, high-temp industrial | Medical, high-flex, high-temp | Aerospace, chemical processing, clean rooms |
PVC (Polyvinyl Chloride) is the most widely used insulation material due to its low cost, ease of processing, and adequate performance for general applications. It is available in a wide range of colors for circuit identification.
XLPE (Cross-Linked Polyethylene) offers improved temperature resistance and mechanical properties compared to standard PVC, making it suitable for power cables and outdoor installations.
PTFE (Polytetrafluoroethylene, known as Teflon) provides the widest temperature range and best chemical resistance of any common insulation. Its high cost limits it to aerospace, military, and high-temperature industrial applications.
Silicone rubber insulation offers outstanding flexibility and high-temperature performance. It is the preferred choice for medical devices, test leads, and applications requiring repeated flexing at elevated temperatures. Its relatively poor abrasion resistance means it often needs additional outer protection.
FEP (Fluorinated Ethylene Propylene) combines many of PTFE’s advantages with better processability. It is used in aerospace, chemical processing, and applications requiring thin-wall insulation for space-constrained routing.
Shielding Types
Shielding protects signal integrity by blocking electromagnetic interference (EMI) and radio-frequency interference (RFI). Shielding is critical for data harnesses, sensor wiring, and any circuits running near power conductors or electric motors.
Foil Shield (Tape Shield): A thin layer of aluminum or copper foil bonded to a polyester carrier, wrapped around the conductors. Foil shields provide 100% coverage and are effective against high-frequency interference. They are lightweight and compact but fragile and difficult to terminate. A drain wire is included for grounding.
Braid Shield: Woven strands of tinned copper or aluminum forming a mesh around the conductors. Braid shields typically provide 70–95% coverage and are effective across a broad frequency range. They are more durable and easier to terminate than foil shields but add more bulk and weight.
Spiral (Serve) Shield: Wires wound in a single direction (not woven) around the conductors. Spiral shields are more flexible than braid shields, making them ideal for cables that must flex repeatedly. However, their shielding effectiveness is lower, typically 70–85% coverage.
Combination Shield: Uses both foil and braid layers for maximum EMI/RFI protection. Combination shields provide near-100% coverage across all frequency ranges and are used in critical instrumentation, medical, and military applications.
Outer Protection Materials
Outer protection shields the wire bundle from mechanical damage, abrasion, heat, chemicals, and environmental exposure. The choice of outer protection depends on the harness routing environment. For design guidance, see our wire harness design guide.
Corrugated Tubing (Split or Unsplit): Flexible plastic conduit, typically made from nylon (PA6 or PA12) or polypropylene. Corrugated tubing provides excellent abrasion protection and is easy to install. Split tubing allows installation over pre-assembled harnesses. Widely used in automotive engine compartments and industrial machinery. Temperature ratings range from -40°C to +150°C depending on material.
Braided Sleeving (Expandable): Woven PET (polyester) or nylon mesh that expands to fit over wire bundles and contracts to grip them. Braided sleeving is lightweight, flexible, and allows easy branch-outs. It provides moderate abrasion protection and is commonly used in electronics, aerospace, and automotive interior harnesses.
Heat Shrink Tubing: Polyolefin or fluoropolymer tubing that shrinks to a tight fit when heated. Heat shrink provides a conformal, sealed barrier against moisture, chemicals, and abrasion. It is used at connector interfaces, splice points, and anywhere a sealed transition is needed. Adhesive-lined heat shrink provides additional environmental sealing.
Spiral Wrap: A helical strip of polyethylene or nylon wound around wire bundles. Spiral wrap allows easy access to individual wires for service and repair. It provides basic bundling and light abrasion protection but does not seal against moisture or contaminants.
Rigid and Flexible Conduit: Metal (galvanized steel, stainless steel) or plastic conduit for maximum mechanical protection. Used in industrial installations, outdoor routing, and areas subject to crushing or impact loads. Liquid-tight conduit combines a metal core with a plastic jacket for both mechanical and environmental protection.
Matching Materials to the Application Environment
The operating environment is the primary driver of material selection. Consider these environmental factors when specifying wire harness materials:
- Temperature: Identify the minimum and maximum operating temperatures. Select insulation and outer protection rated above the maximum expected temperature with a safety margin. For engine-compartment automotive harnesses, materials rated to +150°C or higher are typical.
- Chemical Exposure: Identify all chemicals the harness may contact: fuels, oils, hydraulic fluid, solvents, cleaning agents, or agricultural chemicals. PTFE and FEP insulations offer the broadest chemical resistance. Nylon corrugated tubing resists most automotive fluids.
- UV Exposure: Outdoor-routed harnesses are subject to UV degradation. Use UV-stabilized materials (black nylon conduit, UV-resistant cable ties) or provide secondary UV shielding.
- Vibration: In automotive, aerospace, and industrial applications, constant vibration causes conductor fatigue and insulation wear. Use fine-stranded conductors, flexible insulation (silicone or PVC), and secure routing with adequate strain relief at connector interfaces.
- Moisture and Submersion: For IP67+ requirements, use sealed connectors, adhesive-lined heat shrink, and moisture-resistant insulation. Tinned copper conductors resist corrosion better than bare copper in humid environments.
For definitions of technical terms used in this guide, see our wire harness glossary. Review SIMKAB’s material capabilities and certifications on our quality certifications page.
Need a wire harness engineered with the right materials for your environment? SIMKAB’s engineering team selects optimal conductor, insulation, shielding, and protection materials based on your application’s electrical, thermal, chemical, and mechanical requirements. Request a quote to discuss your project specifications.
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