2. Real conductors have a finite conductivity $\sigma$, and the electric field decreases exponentially inside the conductor, with amplitude decaying as $e^{-z/d}$ for a distance $z$ inside the conductor. The so-called skin-depth can be found (in the approximation of a "good conductor" where $\sigma\gg \epsilon\omega$) as $d\sim \sqrt{\frac{2}{\mu_0\sigma\omega}}$ where $\omega$ is the frequency of the signal in rad/sec. Thus a thickness of a few skin depths will be enough to practically completely stop the field from penetrating through the conductor.