Moroso Jacket

Moroso Spark Plug Wire Jackets: Built for Heat, Built for Performance

When it comes to ignition reliability, the outer jacket of a spark plug wire is the first and most critical line of defense against engine heat, electrical interference, and mechanical wear. Moroso Performance Products has spent decades engineering spark plug wire jackets that hold up in the most punishing race and street environments — and their selection available in the Jacket category reflects that deep expertise.

Dual-Layer EPDM Construction

At the core of Moroso's wire jacket engineering is a dual-layer approach to insulation. The outer jacket is made from two layers of high-heat resistant EPDM (ethylene propylene diene monomer), delivering the best heat protection and highest dielectric strength available in a production spark plug wire. The two EPDM layers are separated by a nylon reinforcing pull tape for added pull strength, ensuring the jacket won't delaminate or stretch during installation or under vibration. This construction means the jacket resists cracking, abrasion, and high-temperature degradation — common failure modes on wires routed near exhaust headers or hot engine bays.

Sleeved and Unsleeved Options

Moroso recognizes that not every build has the same heat management challenges. Wire sets are available with or without exterior sleeving for additional heat protection , letting builders choose the right level of thermal shielding for their specific application. Sleeved jackets are particularly popular for builds with headers or tight engine bay packaging, while unsleeved options keep things clean and lightweight for more moderate environments.

Conductor and Boot Integration

The jacket doesn't work in isolation — it's part of a complete wire system. The efficient conductor is constructed with stainless nickel alloy wire wound around a conductive, latex-coated, heavy fiberglass core, while the inner insulation layer adds optimum dielectric strength and the outer jacket offers superior heat and flame resistance. Silicone plug boots protect against high-heat situations and encase sure-grip, snap-lock terminals for positive connections.

Wire Lines Featuring Premium Jacket Technology

Moroso's jacket technology spans several of their flagship wire families. The Ultra 350 ignition wires are available in 7MM and 8MM diameters and are rated at 350 ohms per foot, making them ideal for daily drivers and performance builds alike. For serious racers, the Ultra 40 Spiral Core series offers 8.5mm wire diameter at just 40 ohms per foot — dramatically lower resistance for maximum spark energy delivery. Ultra 350 wires are proudly made in the USA and offered in vehicle-specific custom-fit sets, as well as universal sets that allow builders to tailor the install for their preferred fitment.

Why Moroso Jacket Products Stand Out

Moroso parts are respected by professional drivers and weekend racers alike for their quality, power, and performance — a reputation built on tracks and roads over generations. Moroso engineers are continually testing and refining their products, taking advantage of new technologies and adjusting to changes in the auto industry to ensure they can continue to compete. For anyone building or maintaining a high-performance ignition system, Moroso's jacket offerings represent a proven, American-made solution with the engineering depth to back it up.