Cable sheathing is necessary to adapt to many different complex climate conditions, but also to ensure long-term (at least 25 years) stability. Cable sheathing not only have a certain strength, low thermal deformation, wear, permeability, heat shrinkage and friction coefficient, but also resistant to environmental stress, material processing performance and so on. Less or with a good jacket material, although through the factory acceptance, but the quality of the existence of defects for some time after the emergence of cracking, seepage, if the use of recycled plastic instead of high quality polyethylene sheathing material is more serious. High-quality sheathing made of fiber optic cable, into the cable after the skin formation, bright, uniform thickness, no bubbles, otherwise there will be cable rough skin phenomenon, and because there are many impurities in the raw materials, fine to see the cable sheath has a lot of very small Pit, and because the thickness is thin, the entire outer diameter of the cable will be much smaller than the quality of the cable. Indoor fiber optic cable, the general use of high-quality flame-retardant PVC, the appearance should be smooth, bright, flexible and easy to peel; otherwise there will be poor skin finish, easy and tight sets of fiber, aramid adhesion phenomenon.