Here are Aloy's bracers from the game Horizon Zero Dawn. This includes both arms and the knee piece. I modeled these off of the official cosplay guide. The knee bracer was kind of hard to see, so I had to guess on some of it.
To add the silvery parts, I used automotive carbon fiber vinyl. I laid a piece over the area I wanted to cover, heated it up a bit with a heat gun, and pressed it down so I could cut the proper shape out with an exacto knife.
The right and left arm pieces are about 7 3/4" long and the knee piece is about 7 1/2" in long.
This was modeled in Fusion 360 with an attached canvas so I could trace the pattern directly.