Is CD case an conductor

• harddisks are constructed from an aluminum platter (conductor) coated with a magnetic metal oxide (insulator)
• floppy discs are constructed from a plastic sheet (insulator) coated with a magnetic metal oxide (insulator)

however the function of computer disks in no way depends on the property of being a conductor/insulator, only on its ability to retain tiny magnetic domains while permitting them to be easily modified.