Copper wiring is the standard material used in the wiring of modern homes. Though aluminum wiring was explored as an option its use was discontinued due to safety concerns. Aluminum expands more than copper and over time this heating up and cooling can result in the wiring creeping out from its terminal causing loose connections and overheating. Additionally, rusting of aluminum wiring can cause overheating. Both issues make aluminum wiring a fire hazard and are not ideal to have. If you have aluminum wiring you should be mindful of these issues.