Recent research has shown that certain infrared (IR) transmitting optical fibers can be used to monitor the chemical changes that occur when a graphite fiber reinforced resin matrix is heated [1–4]. These changes are monitored as a result of the optical fiber behaving as an in situ multiple internal reflectance (MIR) cell. The optical fiber is positioned such that one end of the fiber accepts IR from a suitable source; the other end is positioned such that IR energy is focused into a suitable detector.