Fiber optic cables have an outer insulating jacket made of Teflon or PVC, Kevlar fiber, which helps to strengthen the cable and prevent breakage, plastic coatings, used to cushion the fiber center. The center (core) of the cable is made of glass or plastic fibers.
Source: ANDRESS, Mandy, Exam Cram CISSP, Coriolis, 2001, Chapter 3: Telecommunications and Network Security (page 31).