Since the tube does not have direct contact with the fiber, any cable material expansion or contraction will not cause stress on the fiber. Much of the external stress placed on the tube also will not be transferred to the fiber. The non-hygroscopic gel prevents water from entering the tube. The loose tube cables are proven the best solution for harsh environment conditions in the outdoors.
For higher fiber count, multi-tube structure is made of an assembly of different tubes around a central strength element. Fiber count ranges widely dependent on location of active equipment. The constructions are based on designs with 6, 8 or 12 tubes around the central strength member. For outdoor installation, the cables are designed with resistant outer sheath, generally made of polyethylene to resist to more severe environment constraints (abrasion, temperature variation, crush resistance …). It features a watertight conception, obtained by using jelly and swellable elements, to stop the water propagation within the cable in case of cable accident. Outdoor cables are mainly installed in ducts or directly buried. In some case, Indoor-Outdoor structures are required. They combine the water tightness characteristics and Low Smoke Zero Halogen (LSZH) requirements.