Dielectric Strength

This is an electrical property and gives an indication of how well the material acts as an electrical insulator. It
describes how much of an electrical voltage can be built up on one side of the material before it is communicated to
the other side. Units - Volts per mil of thickness (volts/mil). Higher numbers indicate materials which are better
insulators. C means that the material conducts electricity and therefore has no dielectric strength.

Dielectric constant is a measurement of the quality and electrical properties of the material.

Polyolefins (PE or PP) have a dielectric constant of 2.3. Teflons are 2.07.

http://www.belden-wire.com/faq/faqpdeco.htm

The dielectric constant is defined as the ratio of the permittivity of the material to the permittivity of free space. This is generally measured well below the mechanical resonance. The dielectric constant is derived from the static capacitance measurements at 1 kHz using a standard impedance bridge

equations for http://www.sensortech.ca/eq-dicon.htm