Sarx

Sarx is the incorruptible flesh of Rephaim and other creatures of the Netherworld, called sarx-beings or sarx-creatures.

Description
It has a slightly metallic sheen and is various shades of silver and gold. The flesh itself is difficult to harm and will not age as human flesh would. Not even a bullet can kill the Rephaim. Warden describes sarx as their "immortal flesh. It does not age, nor can it be extensively harmed by amaurotic weapons." It looks like silk.