Roger Russell writes:
Oxygen-free copper (OFC) or Oxygen-free high thermal conductivity (OFHC) copper generally refer to a group of wrought high conductivity copper alloys that have been electrolytically refined to reduce the level of oxygen to .001% or below. Perhaps, it should be more accurately called oxygen reduced copper.
C11000 is the most common copper. It is universal for electrical applications. Electrolytic-Tough-Pitch (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 C11000 sold today will meet or exceed the 101% IACS specification.For the purposes of purity percentage, silver (Ag) content is counted as copper (Cu).