Volume Resistivity vs. Volume Conductivity vs. Surface Resistivity

When cus­tomers look at the tech­ni­cal datasheet (TDS) for LINQSTAT Vol­ume Con­duc­tive Film, they often are con­fused by the elec­tri­cal prop­er­ties. The 3M Velo­stat mate­r­i­al lists only Vol­ume Resis­tiv­i­ty as less than 500 ohm-cm, yet the LINQSTAT mate­r­i­al lists Vol­ume Resis­tiv­i­ty, Vol­ume Con­duc­tiv­i­ty and Sur­face Resis­tiv­i­ty. The fact of the mat­ter is that they are all relat­ed, and if you know the Vol­ume Resis­tiv­i­ty of the mate­r­i­al and the thick­ness of the sheet­ing, then you can cal­cu­late the oth­er values.

Sur­face Resis­tance (also called Sheet Resis­tance) mul­ti­plied times the thick­ness of the mate­r­i­al in cen­time­ters, equals the Vol­ume Resistivity.

Resistance vs. Resistivity vs. Conductivity vs. Conductance

There is such a con­fus­ing mix­ture of resis­tance and resis­tiv­i­ty across the var­i­ous lit­er­a­ture source avail­able both online and offline that one might start to get the idea that these are two dif­fer­ent things. Very sim­ply, a non-elec­tri­cal­ly con­duc­tive mate­r­i­al is said to have a cer­tain resis­tance, and if you are mea­sur­ing this, you are mea­sur­ing the mate­ri­al’s resis­tiv­i­ty. If, on the oth­er hand, the mate­r­i­al is has a very low resis­tance, then it is said to be con­duc­tive, it can have a cer­tain con­duc­tance, and you can mea­sure the mate­ri­al’s conductivity.

Is conductance the opposite of resistance?

Yes. Con­duc­tance is the oppo­site of resis­tance, con­duc­tiv­i­ty is the oppo­site of resis­tiv­i­ty and con­duc­tive is the oppo­site of resis­tive. A low-resis­tance mate­r­i­al can also be said to be con­duc­tive. Since the LINQSTAT Vol­ume Con­duc­tive Film (VCF) mate­ri­als are car­bon-filled plas­tics, where the poly­eth­yl­ene is resis­tive, but the car­bon is con­duc­tive, the films are said to be vol­ume con­duc­tive films.

What is volume conductive?

What is dif­fer­ent in both val­ue and test method is the type of resis­tiv­i­ty being mea­sured. Since the films have a uni­form thick­ness, a prop­er­ty that is often mea­sured is the sheet resis­tance. This prop­er­ty is also called sheet resis­tiv­i­ty, sur­face resis­tiv­i­ty or sur­face resis­tance. All of these are the same, but are dis­tinct­ly dif­fer­ent from a mate­ri­al’s vol­ume resis­tiv­i­ty (also called vol­ume resis­tance, bulk resis­tance or bulk resistivity).

Before we move on to the next sec­tion, let us be sure that we are clear on the following:
Vol­ume Resis­tiv­i­ty = Vol­ume Resis­tance = Bulk Resis­tiv­i­ty = Bulk Resistance
Sheet Resis­tiv­i­ty = Sheet Resis­tance = Sur­face Resis­tiv­i­ty = Sur­face Resistance

Still with me? Ok, let’s go on to explain the dif­fer­ence between these two properties.

Surface (or Sheet) Resistivity vs. Volume Resistivity

Sur­face Resis­tiv­i­ty is a mea­sure­ment of the resis­tiv­i­ty of a mate­r­i­al along the plane or sur­face of the sheet. It is a use­ful mea­sure­ment when mea­sur­ing a thin film of mate­r­i­al with a uni­form thick­ness such as LINQSTAT VCF because it is inde­pen­dent of the mate­r­i­al thick­ness, and can be mea­sured across a range of (thin) thick­ness­es, such as our 2mil, 4mil or 8 mil LINQSTAT VCF films. Sheet resis­tance is expressed as ohms/sq, spo­ken as “ohms-per-square”. This unit is only used for sheet resis­tance because it is dimen­sion­al­ly the same as an ohm, but leaves no room for mis­in­ter­pre­ta­tion as one might mis­take it for the bulk resis­tance otherwise.

Difference between volume or bulk resistivity and surface or sheet resistivity
Bulk (Vol­ume) Resis­tiv­i­ty vs. Sur­face (Sheet) Resistivity

Vol­ume Resis­tiv­i­ty, there­fore is a mea­sure­ment of the resis­tiv­i­ty of a mate­r­i­al per­pen­dic­u­lar to the plane. As such, we can mul­ti­ply the sheet resis­tance by the thick­ness of the mate­r­i­al (in cen­time­ters) to give us a vol­ume resis­tiv­i­ty in “ohms-cm” or ohms-cen­time­ters. Like­wise, the Vol­ume Resis­tiv­i­ty divid­ed by the thick­ness in cen­time­ters equals the sur­face resistivity.

Volume Resistivity vs. Volume Conductivity

Vol­ume resis­tiv­i­ty is also called bulk resis­tiv­i­ty because it is a mea­sure of the resis­tiv­i­ty across a defined thick­ness. As men­tioned ear­li­er, resis­tiv­i­ty is the inverse of con­duc­tiv­i­ty. Since vol­ume resis­tiv­i­ty is mea­sured in Ohms-cm, or spo­ken as “ohms-cen­time­ter”, vol­ume con­duc­tiv­i­ty is one-over-ohm-cm (1/Ω‑cm) and is mea­sured in S/cm, or spo­ken as “Siemen per cen­time­ter”. There­fore, a Vol­ume Resis­tiv­i­ty of 500 ohm-cm is equal to a Vol­ume Con­duc­tiv­i­ty of 1/500 or 0.002 S/cm.

There­fore, look­ing at the LINQSTAT VCF mate­ri­als, this is our “medi­um-lev­el” vol­ume con­duc­tive film and has a the sur­face resis­tiv­i­ty of 10,000 ohm-cm (10^4 Ω‑cm). If you are inter­est­ed in a more con­duc­tive plas­tic, check out of XVCF-Series which has a high­er car­bon-load­ing mak­ing it more conductive.

  • VCF-2xxxxS-Series: 10,000 ohms/square (Sur­face Resis­tance) x 2mil (0.00508cm) = ~50 ohms-cm (Vol­ume Resistance)
  • VCF-4xxxxS-Series: 10,000 ohms/square (Sur­face Resis­tance) x 4mil (0.01016cm) = ~100 ohms-cm (Vol­ume Resistance)
  • VCF-8xxxxS-Series: 10,000 ohms/square (Sur­face Resis­tance) x 8mil (0.02032cm) = ~200 ohms-cm (Vol­ume Resistance)

Why does CAPLINQ give “less than” values (ie. 200,000 ohms per square) instead of Typical Values?

LINQSTAT Vol­ume Con­duc­tive Film is a car­bon-loaded poly­eth­yl­ene. As such, there are nec­es­sar­i­ly some dif­fer­ences in the con­duc­tiv­i­ty over the entire sur­face. The data that CAPLINQ pro­vides is meant to be a min­i­mum, repeat­able val­ue that can be used in the design of the final product.

Watch this video to see how we measure Surface Resistivity vs Volume Resistivity

This video explains the way we mea­sure Vol­ume and Sur­face Resis­tiv­i­ty of our LINQSTAT elec­tri­cal­ly con­duc­tive plastics.

Watch this video to learn the Difference between Surface Resistivity vs Volume Resistivity

This video explains the dif­fer­ence between Vol­ume and Sur­face Resis­tiv­i­ty of our LINQSTAT elec­tri­cal­ly con­duc­tive plastics.

CAPLINQ is a spe­cial­ty plas­tics sup­pli­er offer­ing a range of con­duc­tive mate­ri­als includ­ing our broad range of elec­tri­cal­ly con­duc­tive plas­tics and anti­sta­t­ic tapes and films. If you have any ques­tions, please don’t hes­i­tate to con­tact us to find out how we can help you further.

About Chris Perabo

Chris is an energetic and enthusiastic engineer and entrepreneur. He is always interested in taking highly technical subjects and distilling these to their essence so that even the layman can understand. He loves to get into the technical details of an issue and then understand how it can be useful for specific customers and applications. Chris is currently the Director of Business Development at CAPLINQ.

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