What type of coaxial outer conductor offers the best shielding?

A solid shield, often made of a continuous copper or aluminum tube (as seen in 'Hardline' coaxial cable), offers the best possible RF shielding. Because it is a solid piece of metal, there are absolutely no gaps or holes in the outer conductor to allow RF energy to leak out or external noise to enter. Braided shields, whether single or double, consist of woven wire strands. These weaves naturally leave microscopic gaps that can allow a small amount of RF leakage, especially at higher frequencies. While aluminum foil provides good shielding and is often combined with a braid in consumer cables, a thick, solid metal shield structurally and electrically outperforms all braided and foil variations in terms of RF isolation.