Influence of thermal conductivity of PP-based compounds on surface roughness of rapid heat cycle injection molded parts Thermal conductivity is one of the most important parameters for the formation of surface roughness of injection molded parts. The aim of this study is to gain extended knowledge of the influence of PP-based compounds with different thermal conductivities on the surface of rapid heat cycle molded plastic parts. Therefore, several compounds, comprising glass beads and glass bubbles respectively, were manufactured and injection molded in addition to neat polypropylene. Glass beads are low-priced fillers used to reduce material cost and to improve mechanical properties as well as dimensional stability. Glass bubbles, although at higher cost, are used for similar reasons, but reduce the part weight additionally. Part surface quality is governed by the contact temperature of polymer melt and mold surface. To influence the contact temperature, a change of thermal conductivity of the polymer and alteration of the mold surface temperature are approved approaches. This can be addressed since both fillers significantly alter the thermal conductivity of the material formulation, while rapid heat cycle molding is a common technique to increase mold surface temperature. To gain substantiated information, the amount of filler and the mold surface temperature were varied systematically. To quantify the effect on surface roughness the surface of the mold insert and the part surfaces were measured using confocal microscopy. This allows the determination of the replication of the mold surface into the plastic part surface. Factorial design of experiments enables modeling the RMS surface roughness as a function of filler type and amount, which define the thermal conductivity of the compound, as well as mold surface temperature.