The choice of hanging material is both aesthetic and practical.
Whatever material is chosen must be strong enough to support the panel over a long time.
Chain is reliable and can be obtained in many sizes, styles and metals. You can use a split ring to join the chain to the loops on a panel, or directly if the panel has been fitted with hooks.
Twisted picture wire is a reliable material too. It normally is twisted brass with at least one steel strand embedded. It can be soldered at various points around the panel and at the place where the eye if formed to insure that the twists will not come undone.
Fishing line can be used. You should use the highest test you can find. 50 pound test is sufficient but still not obtrusive. However, it is subject to deterioration with constant light exposure, and so should be renewed every 4-5 years. Also you need to be careful in the knots you use. It is very slippery and a surgeon’s know should be topped up with a second for security.
Fine cable enclosed in plastic can also be used. This is fine enough that it can be tied, but should be joined with knots that cannot slip.