A metal is not a good dielectric. A vacuum is a decent dielectric. There are much better dielectrics than a vacuum. A high dielectric constant, k, means the material exhibits good dielectric behaviour. A vacuum has k = 1, better dielectrics have k > 1. What is the dielectric constant of metals? k = 0? K < 1 ? Doesn't the dielectric constant of a material depend on the frequency of the EM waves pasing through it? Where can I find an expression for the dielectric constant as a function of frequency? I'm confused, please try to unconfuse me. thanks.