My armor and Minute's armor use photogrammetry for the parts that are possible to do that on (so basically no back/cod/kidney as they are not shown in full enough to get a "scan" of so those are hand sculpted). It's a process of using photos of the costume to generate a 3D model then from there it's a lot of clean up and turning into molds. Minute also has some parts (kidney, knees, shoulders, and collar) that are lineage to unused pulls. Basically ILM used existing armor as bucks and pulled over-top of them then Minute cleaned them up and readded the correct dents for each version. Bobamaker is all hand sculpted by him based on reference images.
I also include things like elastic, metal diamond inserts, mirror for the ab plate, chest display film, and other stuff to help put it all together. All of us use ABS plastic I believe all in the same thickness as well.