"Optical fiber consists of a column of glass or plastic surrounded by an opaque outer jacket. The glass or plastic itself consists of two concentric columns. The inner column called the core has a higher index of refraction than the outer column called the cladding."
"Outer Jacket- An outer jacket envelopes the plastic fibers in the cable. It keeps dirt and moisture away from the inner layers, as well as protecting the rest of the cable from cuts and other damage. "