Volume resistivity

Volume resistivity is measured using standardised methods that determine the current flowing through a material specimen and the voltage drop across it. The measurement is usually carried out under defined conditions such as temperature and humidity in order to obtain comparable results.

Formula

Volume resistivity is calculated using the following formula:

ρ = (R × A) / d

• ρ: volume resistivity (Ω·m)

• R: measured resistance (Ω)

• A: area of the electrodes (m²)

• d: thickness of the material specimen (m)

Measuring methods

• Two-electrode method: a DC voltage is applied to two electrodes in contact with the material specimen in order to measure the resistance.

• Testing to IEC 62631: standardised method for measuring the volume resistance of insulating materials.

Volume resistivity is a decisive parameter for evaluating the electrical quality of a material:

• High resistivity: materials with high volume resistivity act as good insulators.

• Low resistivity: materials with low volume resistivity are suitable as conductors or antistatic components.

Various factors can affect the volume resistivity of a material:

• Temperature: for many materials, resistance decreases as temperature rises.

• Humidity: increased humidity can significantly reduce the resistance of hygroscopic materials.

• Material composition: additives such as carbon black or conductive fillers affect resistance.

• Surface condition: roughness or irregularities can distort the measurement results.

Material	Volume resistivity	Properties
Rubber	10⁸ to 10¹³ Ω·m	Excellent insulating capacity
PTFE (Teflon®)	10¹⁵ to 10¹⁶ Ω·m	Extremely high insulation values
Conductive rubber	10⁴ to 10⁶ Ω·m	Antistatic properties
Carbon fibres	10⁻³ to 10⁻² Ω·m	Good conductivity
Polyethylene	10¹⁴ to 10¹⁵ Ω·m	Excellent insulator

Volume resistivity is a central parameter in numerous industries:

Electrical and electronics industry

• Insulating materials: evaluating the insulating capacity of plastics and rubber.

• Conductive materials: use in antistatic components and earthing systems.

Automotive industry

• Seals: electrically insulating rubber seals in vehicle components.

• Antistatic components: use in tanks and lines to prevent electrostatic discharge.

Construction industry

• Cable sheathing: highly insulating materials for electrical cables.

• Coatings: antistatic floor coatings in potentially explosive areas.

Precisely measuring volume resistivity involves some challenges:

• Specimen preparation: uneven surfaces or inaccurate thicknesses can affect the results.

• Environmental conditions: fluctuations in temperature and humidity must be controlled.

• Measuring instruments: high-precision instruments are required to measure very high or very low resistances.

• How is volume resistivity measured? By applying a defined voltage and measuring the resulting current, typically with a two-electrode method.

• Which materials have the highest volume resistivity? Materials such as PTFE or polyethylene have extremely high insulation values.

• Why is volume resistivity important? It is essential for evaluating whether a material is suitable for electrical insulation or conductivity.

• Can volume resistivity be influenced? Yes, resistance can be adjusted by adding fillers such as carbon black or conductive particles.

Volume resistivity is a central parameter in evaluating materials for electrical applications. Whether as an insulator, an antistatic component or a conductive material, precise measurement of this value makes it possible to develop and use materials optimally for specific requirements. Its importance extends from the electrical and automotive industries to the construction and chemical sectors.