Permittivity is a characteristic of matter , and is important in the design and construction of capacitor s and radio-frequency ( RF ) transmission lines. The permittivity of a vacuum (also known as free space) is equal to approximately 8.85 pF/m.
Relative permittivity can be expressed as the ratio of the number of picofarads per meter in a particular substance to 8.85 pF/m. This ratio is called the dielectric constant of a material. Free space has a dielectric constant of 1, and most substances have a dielectric constant greater than this.