An applied electric field induces charges in a dielectric, reducing the field within it.

Field reduction / original field strength = relative permittivity, which depends on frequency

Permittivity = relative permittivity × vacuum permittivity

A material with high permittivity can substantially reduce the electric field within it.

The dielectric constant can be used to assess the polarity of a polymer.

A relative dielectric constant above 3.6 indicates a polar material;

values from 2.8 to 3.6 indicate a weakly polar material;

values below 2.8 indicate a nonpolar material.

C0: capacitance in vacuum

CX: capacitance with a dielectric

The relative static permittivity (or static relative permittivity) of a material under given conditions is a measure of the extent to which it concentrates electrostatic lines of flux. It is the ratio of the amount of stored electrical energy when a potential is applied, relative to the permittivity of a vacuum. The relative static permittivity is the same as the relative permittivity evaluated for a frequency of zero.

The relative static permittivity is represented as εr or sometimes κ or K or Dk. It is defined as

In electromagnetism, relative permittivity, also called the relative dielectric constant, is defined as the ratio of material permittivity (the material's dielectric constant) to vacuum permittivity:

The relative dielectric constant εr is defined as the ratio of εs to ε0: εr = εs/ε0

εr is relative permittivity

εs is the material's static permittivity

ε0 is vacuum permittivity

In vacuum, εs = ε0, so εr = 1

The vacuum reference therefore has a relative permittivity of 1; relative permittivity expresses dielectric behavior as a numerical ratio.

More precisely, the dielectric constant describes the electrical energy stored in an insulator under a static field relative to vacuum, whose relative dielectric constant is 1.

The dielectric constant is therefore also referred to as static permittivity.