Electric Strength - IEC 60243-1
Voltage per unit thickness at which a material will conduct electricity. The higher the value, the more electrically insulating a material is.
The test material is placed between two electrodes. Voltage is increased from 50% of the breakdown voltage to the breakdown voltage at a uniform rate until dielectric breakdown of the material is achieved. Dielectric breakdown is an electrical burn-through (puncture) of the test specimen.