/cgl/ - Cosplay & EGL

I'm working on a cosplay of the main character of Shadow of the Colossus. He wears this weird sort of half-chestplate shoulder armor contraption on top of his shirt and under his surcoat and I'm having a lot of trouble with it. It looks to me like it's made from a stiff material, like thicker leather, but I don't think it'd be possible to make it out of anything stiff without severely limiting my range of motion as it encloses the armpit/shoulder area. How the hell do I make this, /cgl/?