Commercial optical fiber cables use highly purified glass for their cores, glass or polymers for their cladding, and polyurethane for their jackets. Some optical fiber cables use plastic cores, which are cheaper; however, this type of cable has a higher signal loss and works at shorter ranges than glass. Both types transmit light signals using reflection along the axis of the core.
Light entering an optical fiber cable travels long distances using a phenomenon called total internal reflection. Controlling the angle of the light entering the optical cable allows the light to reflect continuously off the surface of the glass and travel along the core. Cores come from highly purified glass extruded into a single fiber and wound onto a spindle. Plastic core optical cables have shorter transmission ranges than those with glass cores, but their greater durability and lower cost make them ideal for use in harsher environments. The cladding provides a material with a lower refractive index that helps shield the light in the core. Cladding can be added as part of the extrusion process or applied later, along with the jacket. Optical fiber cables also have a jacket, which consists of additional layers of polymer coating that provide protection for the core and cladding. Most jackets provide additional padding, called a buffer, and many use Kevlar threads for extra stiffness so the optical fiber cannot bend or break.