I can't remember how thick... I just took the old door to my hardware store and found a sheet that felt right to me
The smaller sheets you get in the hobby bins aren't wide enough so I had to find a larger sheet. I traced it and used tin snips and my Dremel to cut them out
Being that mine is electric after the first flight with the aluminum I could hear them rattle in flight which really bugged me.... I pulled them off and put down thin double sided tape and screwed them back down and now the rattle is gone.