Oxygen-Free Copper vs. ETP Copper: When Does It Matter?
As electrification accelerates across industries, from aerospace and automotive to data infrastructure and advanced electronics, the conversation around copper materials has become more technical. One question engineers and cable manufacturers frequently ask is: Should I be using Oxygen-Free (OF) copper or Electrolytic Tough Pitch (ETP) copper?
Both materials offer excellent conductivity and performance, but understanding their metallurgical differences can help manufacturers select the right material and avoid performance risks in demanding applications.
Understanding the Difference Between OF Copper and ETP Copper
Electrolytic Tough Pitch (ETP) Copper
ETP copper is the most commonly used copper grade in electrical applications today. Produced through electrolytic refining, ETP copper typically contains approximately 99.9% copper with a small oxygen content (~200–400 ppm).
This oxygen exists in the form of copper oxide dispersed throughout the material. For many standard electrical applications, ETP copper performs exceptionally well and delivers conductivity levels around 100% IACS.
ETP copper is widely used in:
Building wire
Power cables
General industrial conductors
Standard automotive applications
For everyday electrical performance, ETP copper remains a reliable and cost-effective solution.
Oxygen-Free (OF) Copper
Oxygen-Free copper is produced using controlled casting methods that minimize oxygen content—typically below 10 ppm. The result is copper with extremely high purity (≥99.99%), improved metallurgical consistency, and enhanced performance in critical environments.
At Sark Wire, our Georgia facility operates an advanced upcasting system, allowing us to manufacture our own oxygen-free copper rod in-house, ensuring strict control over purity, microstructure, and consistency from rod to finished wire.
Key characteristics of OF copper include:
Higher purity copper structure
Reduced oxide inclusions
Improved ductility and formability
Excellent performance in reducing or high-temperature environments
Superior reliability for precision applications
Why Oxygen Content Matters Metallurgically
The primary distinction between OF and ETP copper lies in how oxygen behaves within the metal structure.
In ETP copper, oxygen combines with copper to form microscopic oxide particles. Under most conditions, these inclusions are harmless. However, in certain environments, particularly high temperature or hydrogen-rich atmospheres, they can create challenges.
One well-known phenomenon is hydrogen embrittlement, where hydrogen reacts with copper oxides, potentially creating internal voids that weaken the material.
Oxygen-free copper eliminates this concern by removing oxide formation almost entirely. This becomes important when reliability, thermal stability, or long service life are critical.
When Does Oxygen-Free Copper Really Matter?
Not every application requires OF copper, but it becomes the preferred material when performance margins are tight.
Applications that benefit from OF copper:
Aerospace and defense systems
High-frequency or signal-sensitive cables
Vacuum or controlled-atmosphere environments
High-temperature applications
Semiconductor and electronics manufacturing
EV and advanced power infrastructure
Precision cabling and specialty conductors
In these environments, material purity directly contributes to long-term electrical and mechanical reliability.
The Advantage of Upcast Oxygen-Free Copper Rod
Material performance starts long before wire drawing. It begins at the rod level.
Traditional supply chains often separate rod production from wire manufacturing, introducing variability in chemistry and structure. By producing oxygen-free copper rod through upcasting, manufacturers gain tighter control over:
Copper purity
Grain structure uniformity
Inclusion reduction
Surface quality
Process consistency
At Sark Wire, vertical integration allows us to control the process from copper cathode to finished wire, helping customers achieve consistent performance across demanding applications.
For cable manufacturers and OEMs, this translates into:
Improved drawability
Reduced breakage during processing
More consistent electrical performance
Reliable supply from a domestic source
Choosing the Right Copper for Your Application
The decision between OF and ETP copper ultimately comes down to application requirements. Here’s a breakdown of the possible requirements and the recommended material:
Standard electrical performance = ETP Copper
Cost-sensitive applications = ETP Copper
High reliability environments = Oxygen-Free Copper
High temperature exposure = Oxygen-Free Copper
Advanced electronics or aerospace = Oxygen-Free Copper
Precision manufacturing = Oxygen-Free Copper
Understanding these differences allows engineers and buyers to balance performance, risk, and cost effectively.
Why More Manufacturers Are Moving Toward OF Copper
As industries continue shifting toward electrification, automation, and higher-performance systems, material tolerances are tightening. Many manufacturers are reevaluating conductor materials earlier in the design process to improve reliability and reduce downstream failures.
Oxygen-free copper is increasingly becoming a strategic choice, not just a premium option.
With domestic production capabilities and in-house upcasting at our Georgia facility, Sark Wire supports customers looking for high-purity copper rod and wire solutions built for next-generation applications.
Let’s Talk Copper
If you’re evaluating oxygen-free copper rod for upcoming projects or looking to improve consistency in your manufacturing process, our team is happy to discuss your application requirements and material options.
Contact Sark Wire to learn more about our U.S.-produced oxygen-free copper rod and wire solutions.