Whether you are designing and manufacturing a new cable or simply choosing an existing one for data, power, fiber optics, or industrial automation, the outer sheath (jacket) is much more than just a speaking cover to the eye; it is, in fact, an important job holder in mechanical. Whether you are designing and manufacturing a new cable or simply choosing an existing one for data, power, fiber optics, or industrial automation, the outer sheath (jacket) is much more than just a speaking cover to the eye; it is, in fact, an important job holder in mechanical. fic application. Sheath issues discussed: single jacket versus dual jacket, armored versus unarmored, and metallic versus di lectric armoring. The following issues will play a role in the cable ing environment. It resists water entry while remaining inert to gases and liquids that the cable may be. The main function of the fiber cable outer sheath is to protect the optical fibers in the optical cable from external damage. At the same time, it must have. Polyethylene (PE) optical cable sheath material is an outer protective material designed for optical fiber cables, with excellent mechanical strength, weather resistance and insulation properties. It requires the highest flame retardant rating (UL 910/NFPA 262).