Automotive Wire Loom Materials

Material by Automotive Zone

Map the material to the zone where the harness lives:

Split vs Solid (Convoluted) Loom for Automotive

Split loom is easier to install on an existing harness — push the wires in through the slit and let branches exit wherever needed. However, in high-heat underhood zones the slit can open under thermal cycling, reducing protection. Solid convoluted loom has no slit and resists opening in heat, making it the better choice for exhaust-adjacent and engine-bay runs. For cabin and door harnesses where the risk is low, split loom is the practical choice for speed of installation and ease of branch exits.

For general sizing and material choice, see our wire loom and split loom tubing guide.

Heat-Reflective Sleeving

When the wire harness runs within approximately 6 inches of an exhaust manifold, turbo, or other extreme heat source, loom alone is insufficient regardless of material. Heat-reflective sleeving — typically aluminised fibreglass or similar — wraps over the loom to reflect radiant heat away from the harness. The loom continues to provide abrasion protection; the reflective sleeving handles the radiant thermal load. Use this combination for any underhood run that cannot be re-routed away from the heat source.

Installation Tips for Automotive Wire Loom

Route before you loom. Plan the harness path and test it with the wires bundled but unloomed first — once the loom is on and the harness is tied and secured, rerouting is significantly more work.

Leave service loops. At every connector, branch point, and component, leave 2–3 inches of extra loom so the harness can flex during engine movement and vibration, and so connectors can be reached for service without untying the whole run.

Secure with cable ties at 6–12 inch intervals. Use heat-stabilised nylon cable ties or stainless steel ties in underhood zones. Avoid overtightening, which can close off the loom's flexibility. For loom runs along the firewall or frame, add cable tie mounts or P-clamps at anchor points.

Protect grommets. Where the harness passes through metal panels, use a rubber grommet in the hole and loom up to (not through) the grommet — the grommet provides edge protection; the loom provides the run protection.

Frequently Asked Questions

What type of wire loom should I use in an engine bay?

For general underhood routing, use nylon convoluted tubing, which handles up to about 248°F and resists the fluid splash and vibration of the engine bay. For runs near the exhaust manifold or turbo, use high-temperature nylon convoluted loom (about 300°F) and add heat-reflective sleeving if the run is within about 6 inches of the heat source. Standard polyethylene loom is not suitable for underhood use — it softens above 200°F.

What is the difference between split loom and convoluted loom for automotive use?

Split loom has a lengthwise slit that makes installation on existing harnesses easy, letting branches exit anywhere. Convoluted loom has the same ribbed flexible design but is a closed tube fed from one end — it gives more complete protection because the slit cannot open under thermal cycling. For underhood and engine-adjacent runs where heat and vibration are factors, closed convoluted loom is preferred; split loom is acceptable for cabin and door harnesses where the temperature and abrasion risk are lower.

Can I use standard black wire loom in the engine bay?

It depends on the material. Black polyethylene loom — the most common "standard" loom — has a maximum temperature around 200°F and is not suitable near the exhaust, turbo, or manifold. Nylon loom handles about 248°F and is the better general-purpose underhood choice. For any run adjacent to the exhaust, use nylon or high-temp loom regardless of colour. Colour alone does not indicate temperature rating — always check the material specification.

How do I secure wire loom in an engine bay?

Use heat-stabilised nylon cable ties or stainless steel cable ties in underhood environments — both handle engine-bay heat better than standard nylon ties, which are rated to 185°F. Space ties every 6–12 inches and avoid overtightening, which can kink the loom and restrict the wires inside. For runs along the firewall or frame rail, rubber-lined P-clamps anchored with a screw or bolt are the most secure and vibration-resistant option.

How do I put wire loom on an existing car harness?

Use split loom. Open the slit, press the wire bundle in along the run, and let branch wires exit through the slit where they leave the harness. Secure the loom with cable ties every 6–12 inches and leave 2–3 inches of slack at each connector. For high-heat runs where you can unplug the connectors, closed convoluted loom fed from one end gives better protection.

Conclusion

Engine bay wire loom selection is a temperature decision first and an installation decision second. Map the zone, choose the right material — PE for the cabin, nylon for underhood, high-temp nylon for engine-adjacent — add heat-reflective sleeving near the exhaust, secure with heat-stabilised or stainless cable ties every 6–12 inches, and leave service loops. Get those right and the harness survives the vehicle's life.

Shop polyethylene and nylon split loom and convoluted tubing in our Split Loom Tubing collection. Free shipping over $99, 30-day returns. Call 866-455-8437 for project quantities.