Don't have any copper to use here.
It's a 3/4 inch thick piece of solid aluminum, the same thing that's on my old pot. The old pot seems to work OK but the base simply doesn't have enough mass to hold temps down as I'd want it to while booting or under load. The base on this one is much bigger so I think I'll see a difference between the two pots.
Believe me if I had some copper I'd be using it but gotta go with what I have - That's how it's always been here. Maybe one day I'll get a nice block of it and build something really good.
Not hard to do, just takes time to do it right.