1. Optimize Load For homogeneous elastomers with a durometer (hardness) of around 50-60 shore A, ideal loading is generally around 50 pounds per square inch (psi), although loading of anywhere from 10 - 100 psi may still be effective.
   
   
2. Shape Factor of 0.5 to 1.0 A shape factor of 0.5 to 1.0 proves appropriate for most materials. Changing the thickness of the mount or changing the cross section of the mount changes the shape factor. Rings, strips, or other shapes can be useful in creating the proper shape factor.
   
   
3. Determine the Dynamic Modulus of the Elastomeric The dynamic modulus of the material can be determined using a reduced frequency nomogram. The dynamic modulus of a highly damped material will be affected by temperature and frequency.
   
   
4. Calculate Stiffness Combine shapes to determine the stiffness of complex parts. Many parts can be considered a combination of two blocks, a block and a disk, or any other combination of geometry.
   
   
5. Calculate the Natural Frequency Most systems have a certain frequency of concern from which they must be isolated. This may be the rotational speed of a motor, the blade passing frequency of a fan, and so forth. As a rule of thumb, the natural frequency of the mounting system should be one-third of the frequency of concern.

Reproduced from "The Basics of Vibration Isolation Using Elastomeric Materials" by David Frankovich, former Senior Applications Engineer at Aearo Technologies LLC. Full length whitepaper with formulas can be found here.