1. How Conductivity of Pure Copper Changes with Temperature
The electrical conductivity of pure copper is highly sensitive to temperature. As temperature increases, thermal motion of copper atoms intensifies, which increases scattering of free electrons and therefore reduces conductivity.
At room temperature (20 °C), pure copper has extremely high conductivity.
When temperature rises, conductivity decreases almost linearly.
When temperature drops, conductivity increases significantly.
The temperature coefficient of resistance for pure copper is approximately 0.00393 per °C. This means that for every 1 °C increase in temperature, the resistance of copper increases by about 0.393%, and conductivity decreases accordingly.
At extremely low temperatures, such as in a cryogenic environment, pure copper shows nearly superconducting-like conductivity. In high-temperature conditions close to its melting point, conductivity drops to a very low level. This negative correlation between temperature and conductivity is a key factor considered in electrical design, especially for high-current cables, transformers, and electrical contacts that generate heat during operation.
2. Conductivity and Resistivity of Pure Copper
At 20 °C, the standard electrical properties of pure copper are defined as follows:
Electrical resistivity: 1.7241 × 10⁻⁸ Ω·m
This is the internationally accepted standard value for high-purity copper.
Electrical conductivity: Approximately 58.0 MS/m (megasiemens per meter)
IACS conductivity: 100% IACS
IACS (International Annealed Copper Standard) is the most common unit for expressing conductivity in the metal industry. By definition, standard fully annealed pure copper equals 100% IACS. This value serves as the reference for all other conductive materials. For example, aluminum is about 61–62% IACS, while brass is only 20–30% IACS.
These values apply to high-purity copper with purity above 99.95%. Even small amounts of impurities will lower conductivity and increase resistivity.
3. Conductivity Differences Among Different Pure Copper Grades
There are several common grades of pure copper, and their conductivity differences are relatively small but noticeable in precision applications.
Electrolytic Tough Pitch Copper (ETP Cu, C11000)
Most widely used, purity about 99.90%.Conductivity: 97%–100% IACS
Used in cables, busbars, motors, and general electrical components.
Oxygen-Free Copper (OFC / C10100)
Purity above 99.99%, very low oxygen content.Conductivity: 100%–101.5% IACS
Slightly higher than ETP copper, used in high-frequency devices, vacuum electronics, and precision conductors.
Phosphorus Deoxidized Copper (DHP Cu, C12200)
Deoxidized with phosphorus, good for welding and brazing.Conductivity: 85%–90% IACS
Lower than ETP and oxygen-free copper due to phosphorus content, mainly used in pipes, heat exchangers, and plumbing components rather than high-efficiency conductors.
In summary：
Oxygen-free copper has the highest conductivity.
ETP copper is close to 100% IACS and cost-effective.
Phosphorus-deoxidized copper has obviously lower conductivity but better processability.
For general electrical and electronic applications, ETP copper is sufficient. Only in high-precision, high-frequency, or ultra-low-temperature environments is oxygen-free copper necessary.
