What is the difference between a jacketed and an unjacketed optical fiber?

The major difference between jacketed and unjacketed optical fibers is durability. Because transmission through an optical fiber is dependent upon the reflection of light off the cladding, any nicks or scratches in the cladding could cause back-reflections and light loss. Jacketed fibers help prevent any damage to the cladding. Jacketed fibers are recommended in applications where there is a possibility of even minor damage to the fiber. Unjacketed fibers are recommended for applications where a jacketed fiber's larger diameter or heavier weight are not practical. Unjacketed fibers are also known as fiber strands, whereas jacketed fibers are also known as light guides. Jacketed fibers can consist of one or more fiber strand and the jacket coating is typically a black polyethylene material.