their scrap. I scored a ~3"x8"x1/8" piece for free. I wasn't so successful with the car toys d-bags that gave me the "we can't give out shop materials" line. I told them they can charge me a few bucks if they'd like but I'm asking for scrap, something, they're throwing away. Finally he came back with about the same size as above but 1/4" thick.
My experience, as Bernie mentioned is that 1/8" would be ideal. As for the din, I would think 1/16" would be better if they make it.... I found that after mounting my AVC-R, that the center console is very tight to snap in on opposite ends of the clock. I had to actually shave away the backside of the ABS sheet since I didn't want to shave down the din pocket that I reused.