This property is useful in capacitor s, especially at radio frequencies. Dielectric materials are also used in the construction of radio-frequency transmission lines. In practice, most dielectric materials are solid. Some liquids and gases can serve as good dielectric materials. Dry air is an excellent dielectric, and is used in variable capacitors and some types of transmission lines.
Distilled water is a fair dielectric.
A vacuum is an exceptionally efficient dielectric. An important property of a dielectric is its ability to support an electrostatic field while dissipating minimal energy in the form of heat. Another consideration is the dielectric constant , the extent to which a substance concentrates the electrostatic lines of flux. Substances with a low dielectric constant include a perfect vacuum, dry air, and most pure, dry gases such as helium and nitrogen. Materials with moderate dielectric constants include ceramics, distilled water, paper, mica, polyethylene, and glass.