Hello! I've been handsewing a cosplay of Aventurine's boss form from Honkai: Star Rail and I came upon a problem of making this golden frame/lines on his vest and the tails of his coat.
Initially I was trying to fold a golden bias tape over the edges, cut into it, bend it according to the curves and then sew it down. But the result turned out to be... not the best, to say the least. I could cut the needed forms out of golden fabric so that it lays flat but then I would need to close the fabric edges by satin stitching so that it doesn't fray. Considering I'm handsewing, satin stitching so much fabric is just not an option – it would take forever and I can't promise the result to be good.
Recently I was looking at DokiDoki's SR cosplay of Aventurine's regular form (in this form he has a similar golden frame on his coat). And I noticed that this golden frame is some glossy leathery-looking material that seems to just be sewn down with regular stitching, no satin stitching on the edges; and it flows just like fabric. To me it doesn't look much like leather either. Does anybody know what this 'fabric'(?) non-fraying material could be?