How to Choose the Correct Sorbothane® Durometer and Shape

December 21, 2015

What is Durometer?

Durometer is a measurement of relative stiffness and is used to compare polymers. 
Sorbothane® is softer than rubber and most other polymers. Sorbothane® is measured on the Shore “00” scale. Most types of rubber and other polymers are specified using the Shore “A” or Shore “D” scales. In comparing stiffness, be aware of the scale being used for the material in question. The hardness comparison values listed are approximate and should only be used as a guide.

Reduction of Hazardous Substances (RoHS)

Sorbothane itself and all standard Sorbothane products meet RoHS compliance per EEC directives.

What are Shape Factors?

Shape Factor is a term of art used in the design of elastomer products. It has the virtue of being an easily developed mathematical expression. It quantifies the unique ability of elastomers to react to an applied force by bulging at 90 degrees to the direction of application of the force. A “high” shape factor indicates a minimal ability to deform. A “low” shape factor indicates a soft material with a high ability to deform. Implicit in a low shape factor is a low spring rate and the capability to have a low natural frequency. 

The Shape Factor is calculated by developing the ratio of the average contact surface (one side) divided by the perimeter area. 

As such, it can be developed for any shape that can be mathematically described. However, a few standard shapes cover over 90% of all needs. 

Product properties developed using the Shape Factor methodology have a nominal accuracy of +/-15%. More precise product properties require physical testing or Finite Element Analysis (FEA).

Recommended Maximum Compression of Sorbothane

(These values are for static fatigue conditions. Dynamic and short-term deflections may exceed these numbers by considerable amounts.)

Shape Factor Deflection (% of free height)
0 through 1.0 20
+1.0 to 1.6 10
+1.6 to 2.0 5
+2.0 3

Calculating Deflection / Natural Frequency / Spring Rate

Sorbothane offers the Engineering Design Guide, a Windows-based design program. 
It may be downloaded from the website here. A PDF version is also available from the site. In addition, a printed version of the Engineering Design Guide is available upon request from the factory.