The relative permeability of a dielectric is defined in terms of the magnetic permeability
The corresponding quantity for electricity is called the dielectric constant
Dielectric, Dielectric Constant, Magnetic Susceptibility, Permeability of Free Space
References
Bekefi, G. and Barrett, A. H. Electromagnetic Vibrations, Waves, and Radiation. Cambridge, MA: MIT Press, p. 420, 1987.
