Understand the Resistance!

Simplified Explanation of the Resistivity Properties in Plastics

Resistance and resistivity are pertinent in defining a plastic material's ability to provide electrostatic shielding or the dissipation of an electrical charge. The issue is that these two values are not interchangeable and often lead to confusion. In addition, it becomes more complex when you compare surface vs volume resistance values. Understanding the "resistance" property that best suits your application's unique needs is critical. In this article, we will draw a simple distinction between the "resistance properties".

Surface Resistance

Surface Resistance is defined by the ratio of a Direct Current (DC) voltage to the current flowing between two electrodes of a defined configuration in contact with the same side of the polymer material. Surface resistance tests measure the capacity of a plastic material to restrict the flow of electricity. This test can be dependent on conditions such as humidity, thickness of the sample, and temperature of testing. The unit of measurement is Ohms.

Surface Resistivity

Surface Resistivity is the more common test for plastics when evaluating ESD properties for an application and is a standard property of a material that is not influenced by the shape of the electrodes or the distance between them such as with Surface Resistance. Surface Resistivity is defined as the electric current flowing across the surface as the ratio of DC voltage drop per unit length to the surface current per unit width. Essentially, Surface Resistivity is a measure of the electrical resistance across a unit square surface of material and is a means for classifying materials as conductive, static dissipative, or insulating. Surface Resistivity is measured in Ohms / sq.

Volume Resistivity

Like Surface Resistivity, Volume Resistivity is a standard property of a material. It differs however in that it is measured between two electrodes on opposite faces of the material with the distance standardized. Volume Resistivity measures the polymer's resistance to leakage as an insulator or level of conductivity through the body of the material. Volume resistivity is useful for evaluating the impact of the relative dispersion of a conductive additive throughout the polymer matrix.