Although an optical fiber is very thin, it is composed of two kinds of glass and a protective outer shield. Specifically, these are the:

Although susceptible to sharp bends, the properties of the core and cladding have been altered at the molecular level to make it very strong. Optical fiber is proof tested through a rigorous manufacturing process for strength at a minimum of 100,000 pounds per square inch. Optical fiber is durable enough to withstand handling during installation and deployment in harsh environmental conditions in networks all around the world.