A protective coating of one or two layers of cushioning material, such as acrylate, encases the cladding and helps preserve the optical integrity of the fiber. This sheath reduces crosstalk between adjacent fibers and loss-increasing microbending that occurs when fibers are pressed against rough surfaces. An optical fiber cable buried in the ground typically contains 100 or more fibers bundled together.
By packing more colors (wavelengths) of light into its core, an optical fiber can carry more bits of data. The refractive index of the core is higher than that of the cladding. The total reflection of the light beam caused by the difference in the refractive index (density) of the fiber core and cladding keeps the light wave contained in the core.