Oxygen-free copper is refined copper ore that includes around 0.001% oxygen. Since raw copper has impurities, it must be refined, which introduces oxygen into the mix. Oxygen-free copper is the result of using a refinement based on copper sulfate and sulfuric acid.2 Oxygen-free copper supposedly increases conductivity in wires of over 50 feet, but it’s not noticeable at shorter lengths. The big takeaway from OFC is that you want a cable that uses pure copper, and OFC is close to that level. You have a better chance of reducing signal loss by choosing cables with OFC wires than those with copper-clad aluminum wires.