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# 10.1: Permittivity of Some Common Materials

The values below are relative permittivity $$\epsilon_r \triangleq \epsilon/\epsilon_0$$ 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 $$\epsilon'$$ or $$\epsilon_r'$$) 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): $$\epsilon_r \triangleq 1$$

Table $$\PageIndex{1}$$: Solid Dielectrics:
Material $$\epsilon_r$$ Common uses
Styrofoam$$^1$$ 1.1
Teflon$$^2$$ 2.1
Polyethylene 2.3 coaxial cable
Polypropylene 2.3
Silica 2.4 optical fiber$$^3$$
Polystyrene 2.6
Polycarbonate 2.8
Rogers RO3003 3.0 PCB substrate
FR4 (glass epoxy laminate) 4.5 PCB substrate

$$^1$$ Properly known as extruded polystyrene foam (XPS).
$$^2$$ Properly known as polytetrafluoroethylene (PTFE).
$$^3$$ Typically doped with small amounts of other materials to slightly raise or lower the index of refraction ($$=\sqrt{\epsilon_r}$$).

Non-conducting spacing materials used in discrete capacitors exhibit $$\epsilon_r$$ ranging from about 5 to 50.

• Semiconductors commonly appearing in electronics – including carbon, silicon, geranium, indium phosphide, and so on – typically exhibit $$\epsilon_r$$ in the range 5–15.
• Glass exhibits $$\epsilon_r$$ in the range 4–10, depending on composition.
• Gasses, including air, typically exhibit $$\epsilon_r\cong 1$$ to within a tiny fraction of a percent.
• Liquid water typically exhibits $$\epsilon_r$$ in the range 72–81. Distilled water exhibits $$\epsilon_r \approx 81$$ at room temperature, whereas sea water tends to be at the lower end of the range.
• Other liquids typically exhibit $$\epsilon_r$$ 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 $$\epsilon_r$$ in the range 2.5–3.5 when dry and higher when wet. The permittivity of soil varies considerably depending on composition.