What are the differences between oxygen-free copper (OFC) and oxygen-containing copper (ETP)? 

Why is oxygen-free copper chosen for high-end wiring harnesses?

The biggest difference between oxygen-free copper (OFC) and oxygen-containing copper (generally called ETP copper, Electrolytic Tough-Pitch Copper) lies in the "oxygen content" and "purity" of the materials. Oxygen-containing copper naturally absorbs a small amount of oxygen during the refining process, with an oxygen content of approximately 200-400 ppm. This results in the formation of trace copper oxide (Cu₂O) particles within the material. These oxides reduce grain integrity, making electron transport more susceptible to interference, leading to slightly lower conductivity and a greater likelihood of performance degradation due to oxidation over long-term use.

In contrast, oxygen-free copper is smelted in a vacuum or hydrogen-protected atmosphere, with the oxygen content controlled below 10 ppm. The material contains almost no copper oxide, resulting in higher purity, a more complete crystal arrangement, and less obstruction to electron transport. This gives oxygen-free copper higher conductivity (up to 101% IACS or higher), lower impedance, and better signal integrity, while also making it more heat-resistant and less prone to embrittlement. These advantages make oxygen-free copper the preferred material for high-end applications such as high-speed AI server cables, precision instruments, high-speed automotive communication cables, and audio cables.