What are the properties of copper and aluminum, besides cost, that favor selecting one over another for antennas, ground cables, etc? What difference does it make electrically, efficiency wise, if any? If one was building an wire antenna, would it make a difference to use aluminum wire vs the same size copper? What about yagis? Those are built from aluminum tubing, mostly. Assuming cost was no object, would copper result in a better performance? These questions are not entirely theoretical. I am planning a salt water counterpoise for my BigIR vertical which will sit on the dock behind the house, in a channel off San Diego Bay. The idea is to encase a sheet of metal in plexiglass, sealed, mounted to be in the water and connected to the vertical as a ground/counterpoise/radial substitute. Copper foil is about $10/s.f. Aluminum isn't. Will it matter?