I think isolated means insulated. It depends on the frequecy that the inductor is being used at. Most inductors are wound with magnet wire, which is solid copper wire with some form of enamel on the wire for insulation. At low RF frequencies Litz wire is used. It consists of very small diameter(large guage number)with many strands in parallel. This helps reduce the self capacitance of the coil. I have used solid hookup wire with insulation, and have used buss bare wire for other applications.
There are times when silver plated wire is used.