To shorten development times of complex injection molded parts, pre-series parts are usually manufactured. For this purpose, aluminum is used for pre-series molds. By using additive manufactured injection mold made of plastics, molding costs for pre-series can be drastically reduced and manufacturing time of a fully functional injection mold can be greatly shortened. A major challenge is injection molding of glass fiber reinforced polymers in additive manufactured molds. Up to now, it is not possible to injection mold more than 60 parts with glass fiber reinforced polymers, using an additive manufactured mold [1][2]. Ordinarily, immediate destruction of the additive plastic mold occurs when injection molding glass fiber reinforced polymers [3]. In this study, glass fiber reinforced technical polymers are processed in additive manufactured mold inserts made of plastics. Here, the mold inserts are fabricated by using the FFF process and different types of plastic filaments are used. In addition to mold life during injection molding, temperature control concepts of the mold inserts, achievable cycle times in injection molding and typical dimensional deviations of the manufactured molded parts are investigated. It can be shown that more than 1000 glass fiber reinforced molded parts can be produced from a single mold insert made of plastics. These quantities are also suitable for small batch production. [1] N.N.: Choosing the Right Material for Injection Molds. Minnesota (US): Stratasys, Ltd., 2015. [2] N.N.: Buying time with 3D printed tooling. Zimmern / Rottweil: Wehl & Partner Muster und Prototypen GmbH, 2016. [3] Kampker A. et al: Almeida H., Vasco J. (eds) Progress in Digital and Physical Manufacturing. ProDPM 2019, pp. 28-39.