/cgl/ - Cosplay & EGL

Hello! I am new to advanced garment sewing but have made a lot of armor cosplays over the years ranging from casting resin to EVA foam. I have taken sewing classes throughout early highschool but they mostly had a focus on quilting nad not drafting patterns or garment construction.

I am currently making an undersuit for one of my sci fi suits, and was intrigued by Lightning Cosplay's recent undersuit post as I hope to achieve a similar look with the side turquoise parts on the legs. Would anyone be able to give me advice on how they are constructed?
From my knowledge is seems that turquoise fabric has batting underneath and is sewn to the hexagon fabric and lower back fabric, and the black alternating lines on the turquoise fabric are topstitched on. I am not sure if this is correct hough, as I have seen similar construction with GSTQ's latest bodysuit where everything is sewn together like a large puzzle and it doesn't seem as if anything was topstitched or heat n bonded on.

Thanks guys! Im starting to realize how in-depth Garment sewing is with facings, understitiching, and how complex lining and some pattern darting can get. Its not just as simple as draping and adding seam allowance....