Oxygen-free copper (OFC) or oxygen-free high thermal conductivity (OFHC) copper is a group of wrought high-conductivity copper alloys that have been electrolytically refined to reduce the level of oxygen to 0.001% or below. Specification Oxygen-free copper is typically specified according to the ASTM/UNS database. The UNS database includes many different compositions of high conductivity electrical copper. Of these, three are widely used and two are considered oxygen-free: C10100 – also known as oxygen-free electronic (OFE). This is a 99.99% pure copper with 0.0005% oxygen content. It achieves a minimum 101% IACS conductivity rating. This copper is finished to a final form in a carefully regulated, oxygen-free environment. Silver (Ag) is considered an impurity in the OFE chemical specification. This is also the most expensive of the three grades listed here. C10200 – also known as oxygen-free (OF). While OF is considered oxygen-free, its conductivity rating is no better than the more common ETP grade below. It has a 0.001% oxygen content, 99.95% purity and minimum 100% IACS conductivity. For the purposes of purity percentage, silver (Ag) content is counted as copper (Cu). C11000 – also known as electrolytic-tough-pitch (ETP). This is the most common copper. It is universal for electrical applications. ETP has a minimum conductivity rating of 100% IACS and is required to be 99.9% pure. It has 0.02% to 0.04% oxygen content (typical). Most ETP sold today meets or exceeds the 101% IACS specification. As with OF copper, silver (Ag) content is counted as copper (Cu) for purity purposes. Oxygen-free high thermal conductivity Oxygen-free high thermal conductivity (OFHC) copper is widely used in cryogenics. OFHC is produced by the direct conversion of selected refined cathodes and castings under carefully controlled conditions to prevent contamination of the pure oxygen-free metal during processing. The method of producing OFHC copper ensures an extra high grade of metal with a copper content of 99.99%. With so small a content of extraneous elements, the inherent properties of elemental copper are brought forth to a high degree. In practice the oxygen content is typically 0.001 to 0.003% with a total maximum impurity level of 0.03%. These characteristics are high ductility, high electrical and thermal conductivity, high impact strength, good creep resistance, ease of welding, and low relative volatility under ultra-high vacuum. Standards Conductivity is generally specified relative to the 1913 International Annealed Copper Standard of S/m. Advances in the refining process now yield OF