• Electromagnetics I
• Ch 10
• Loc 10.1

# Permittivity of Some Common Materials

The values below are relative permittivity

for a few materials that are commonly encountered in electrical engineering applications, and for which permittivity emerges as a consideration. Note that “relative permittivity” is sometimes referred to as dielectric constant.

Here we consider only the physical (real-valued) permittivity, which is the real part of the complex permittivity (typically indicated as

or

) for materials exhibiting significant loss.

Permittivity varies significantly as a function of frequency. The values below are representative of frequencies from a few kHz to about 1 GHz. The values given are also representative of optical frequencies for materials such as silica that are used in optical applications. Permittivity also varies as a function of temperature. In applications where precision better than about 10% is required, primary references accounting for frequency and temperature should be consulted. The values presented here are gathered from a variety of references, including those indicated in “Additional References.”

Free Space (vacuum):

MaterialCommon uses
Styrofoam11.1
Teflon2
2.1
Polyethylene2.3coaxial cable
Polypropylene2.3
Silica2.4optical fiber3
Polystyrene2.6
Polycarbonate2.8
Rogers RO30033.0PCB substrate
FR4 (glass epoxy laminate)4.5PCB substrate

1Properly known as extruded polystyrene foam (XPS).

2Properly known as polytetrafluoroethylene (PTFE).

3Typically doped with small amounts of other materials to slightly raise or lower the index of refraction (

).

Non-conducting spacing materials used in discrete capacitors exhibit

ranging from about 5 to 50.

• Semiconductors commonly appearing in electronics – including carbon, silicon, geranium, indium phosphide, and so on – typically exhibit in the range 5–15.
• Glass exhibits in the range 4–10, depending on composition.
• Gasses, including air, typically exhibit to within a tiny fraction of a percent.
• Liquid water typically exhibits in the range 72–81. Distilled water exhibits at room temperature, whereas sea water tends to be at the lower end of the range.
• Other liquids typically exhibit in the range 10–90, with considerable variation as a function of temperature and frequency. Animal flesh and blood consists primarily of liquid matter and so also exhibits permittivity in this range.
• Soil typically exhibits in the range 2.5–3.5 when dry and higher when wet. The permittivity of soil varies considerably depending on composition.