 Materials can be classified according to their complex-valued permittivity , upon comparison of its real and imaginary components (or, equivalently, conductivity, , when accounted for in the latter).A "perfect conductor" has infinite conductivity, , while a "perfect dielectric" is a material that has no conductivity at all, ; this latter case, of real-valued permittivity (or complex-valued permittivity with zero imaginary component) is also associated with the name "lossless media".Generally, when we consider the material to be a "low-loss dielectric" (although not exactly lossless), whereas is associated with a "good conductor"; such materials with non-negligible conductivity yield a large amount of loss that inhibit the propagation of electromagnetic waves, thus are also said to be "lossy media".