The quality of the parts in the mechs is mainly determined by the material as well as the craftsmanship. And as these aspects of parts-production come into light, the metallic materials holds an absolute advantage compared to other materials existed, which hence, the majority of the mech parts being made out of metals today.
However, a subject had arisen among those maniacs over mech parts in the Nine Gates city recently…
"Skeleton? You mean those parts were made out of skeletons? How was their performance? Have you seen the actual product?"