Interdigital sensors (IDS) have received great attention for production monitoring of polymers over the past decade. However, conventional IDS are limited by high noise to environment due to the dual side access of the sensor, low nominal capacitance, and sensitivity. In this study, a shielded IDS fabricated by flexible circuit board (FCB) technology is presented to overcome these challenges. Compared to conventional sensors, the environmental dependence of the new sensor is minimized by the copper shield. Furthermore, nominal capacitance of at least 350% higher, and an increase of sensitivity per unit area are achieved. To demonstrate the capabilities of the new IDS, a FCB comprising the proposed sensor is fabricated, attached to a mould, and successfully applied for in situ real-time production monitoring of an epoxy resin. The resulting flexible sensor is noninvasive towards the fabricated parts, and measures the key stages along the production process. (C) 2016 Wiley Periodicals, Inc.