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In this work, we propose a combined computational and experimental study to investigate the effect of bidispersity of polyethylene (PE) chains on the interface and interphase between the polymer and carbon black (CB) filler particles. To reach this goal, we have implemented a molecular description based on hybrid particle–field modeling approach that allows to perform large-scale simulations of CB primary particles of realistic size (20 nm) embedded in bidisperse PE melts of high molecular weight and simulated as large-scale models up to about two million coarse-grained units (beads). Due to the molecular detail of the proposed models, we are able to provide an accurate representation of the local structure of PE chains adsorbed on different surface sites of CB primary particles. Experiments performed with the Borealis technology Borstar to synthesize bimodal PE, together with simulations of bidisperse PE melts, provide a possible molecular mechanism involving short PE chains able to explain the improved dispersion of CB in bimodal polymer melts. The achieved insights can help in the design of new and optimized ternary mixtures.