Fiber-optic cables send light signals down a glass or plastic fiber thinner than a strand of hair. Reflective cladding surrounding that core boosts the signal in a technique called "total internal reflection." The speed of the light passing down the cable is determined by the index of refraction in the core, which traps the light at an optimal angle for speed. The outermost part of the cable is called the buffer, which protects the fiber from physical damage.