Almost all injection molds have multi-cavity runner system for mass production, which are designed with geometrically balanced runner system in order to accomplish filling balance between cavity to cavity during processing. However, even though geometrically balanced runner is used, filling imbalance has been observed. Filling imbalance could be decreased by modifying processing conditions such as injections rate, mold temperature, injection pressure, melt temperature that are related to shear, viscosity. In this study, a series of experiment was conducted to investigate filling imbalance variation when modifying runner layout and polymer and to determine which processing condition influences as the primary cause of filling imbalance in geometrically balanced runner system. The filling imbalance was decreased up to result range of $3{leq}DFI{leq}8(%)$ by using a new runner system for balanced filling.