Aluminium Wires
Insurance companies don’t like aluminum electrical wiring. It’s not technically the wires that are the problem, but the connectors used to join the wires. Because aluminum is soft, the wires come loose from common connectors and can cause a short-circuit.
If you have aluminum wiring in your house, you can mitigate the risk by replacing all of your connectors with the correct kind. Make sure the connectors are rated correctly for the two types of metal you are connecting. For example, copper-to-aluminum connectors are likely not safe for use with an aluminum-to-aluminum connection.