You can’t build a circuit without wires.  We have two common types: Aluminum and Copper.   Copper is more expensive to use but much better.   Copper melts 423K higher than aluminum.   Aluminum expands and contracts more than copper. 

It’s often preferred, in fact, over aluminum wiring because of its high tensile strength. The tensile strength of copper is roughly 40% higher than that of aluminum. With a higher tensile strength, copper wiring is less likely to break than aluminum wiring.

General rule is that Aluminum conductor that carries the same current as copper is two (2) sizes larger. Example #14 ga copper = #10 ga aluminum or copper clad aluminum. General house/home wiring, you would seldom see Aluminum conductor under #6 in size, most often used for electric range/dryer/smaller AC.