I just saw this picture of wire.
Pirelli Cable-X - 500 MCM Type THHN or THWN-2 600V Gasoline & Oil Resistant II AWM (UL)
Wait a minute.
It's routine common THHN, like you might use in a 250A service or something. But despite all this detail it seems to have forgotten to state whether it is copper or aluminum. And tell you the truth, I've never stopped to notice if any of my other THHN also fail to mention.
The UL publishes a guide on wire and cable markings:
UL Marking and Application Guide https://www.ul.com/wp-content/uploads/2014/04/WC_MG.pdf
Conductor Material
Compact stranded copper conductors are identified by “compact” or “cmpct,” otherwise wire and cable with bare or coated copper conductor material is not marked with stranding identification.
If the conductor material is either aluminum or copper-clad aluminum, the product, tag or carton markings (depending on the product category) identify the conductor material. These markings will appear as “AL,” “ALUMINUM,” “AL (CUCLAD),” “ALUMINUM (COPPER-CLAD),” “CU-CLAD AL” or “COPPER-CLAD ALUMINUM.” For some wire and cable, other metals may be used as conductor material. The associated markings for that wire and cable are explained under the heading “OTHER.”
The "default" is indeed copper.
However, the AWM in the marking would lead me to believe this may be something other than building wire per NEC:
This guide does not address wire and cable evaluated only for suitability as factory-installed component wiring in other Listed equipment. Those products are Recognized by UL under the Component-Appliance Wiring Material (AWM) and Component-Nonshielded cable categories and are not identified with an NEC® wire Type designation.
