Practically, metals used in antennas and their surroundings are not perfect electric conductors. To accurately design an antenna, ohmic loss effects should be accounted for.

Finite conductivity is accounted for by computing the equivalent surface impedance of the metal. It is important to note that the thickness applied to metallic or dielectric faces is not a physical thickness. It is only used to determine the surface impedance.

The video in this article explains in more details the way the thickness is modeled for this type of metals and includes an example of shielding of a finite conductivity sphere.