Texas, we are pretty much required to use a copper wire.
The rod itself is almost always steel- though the copper cladding makes it look like it's made of cooper.
What is copper cladding? Simple: a copper tube is heated up to expand it, a steel rod is inserted, and the copper shrinks to the rod as it cools. This is much more copper than you would get by simply plating the rods. How are the ends sealed? I don't know.
We have galvanized steel rods, stainless steel rods ... indeed, most any material can be used for a rod. The copper clad steel rod is by far the most common.
