A slick ribbon of black steel.  The ring diameters have been carefully chosen to make the densest possible weave, so that the matte surfaces of the tightly woven rings make no noise when they move.  Go sneak up on someone.

(For the record, I support the pirates.)

20 ga. 3/16" and 5/32" ID
Black annealed steel
European 6:1 snakeskin