Rubber is often used as an electrically insulating material and, correctly formulated, it can offer outstanding properties in this respect. However, electrical properties are dependent on the materials used in compounding and requirements should be clearly defined.
In general, an insulating material can be defined as having an electrical resistance greater than 100 megohms per cm3. Materials for applications requiring extremely good insulating properties are usually defined by electric strength, measured in Kilovolts (KV) per mm thickness of material. This is calculated by placing a sheet of the material between two electrodes and applying an increasing voltage until electrical breakdown occurs.
Good insulation is achieved by the use of non-black fillers, and compounds of any colour which are based on these fillers are suitable for insulation purposes.
For test methods and recommended resistance values for anti-static and conductive rubbers, please see BS 2050.