A dielectric monitoring system has been developed for the real-time sensing of composite manufacturing processes of reactive thermoplastic materials. In addition, optimised durable non-intrusive interdigitated dielectric sensors have been designed and manufactured for the sensing of resin arrival, viscosity changes as well as material transformtion and crystallisation. The dielectric sensors receive the appropriate AC stimuli from the monitoring system while the feedback is recorded and processed by the system providing real-time material state-based information (viscosity, degree of reaction etc.). The system and the sensors were used successfully to monitor the infusion of glassfibre with CBT oligomers and their reaction to form PBT at the end of the process.