This work investigates high-density polyethylene (HDPE) composites reinforced with calcium carbonate (CaCO₃), highlighting the importance of Masterbatches for efficient dispersion of CaCO₃ in the polymer matrix. The preparation of the Masterbatches resulted in a homogeneous mixture, optimizing processing conditions and stabilizing the mechanical and thermal properties of the composite, even with high filler ratios.The addition of CaCO₃ up to 20% via a concentrate improved the flowability index, facilitating composite processing, while maintaining a stable Vicat temperature, a sign of uncompromised thermal resistance. Infrared analyses confirmed a homogeneous dispersion of CaCO₃ in the polymer matrix.Mechanically, composites with up to 15% CaCO₃ via concentrate retained satisfactory properties while improving processability. However, at 20%, a reduction in ductility is observed, although stiffness and mechanical strength remain preserved. This indicates that the composite becomes less deformable before fracture at high loading rates.