In the present study, it is demonstrated that the stereoregularity of the copolymer fraction of bimodal high-density polyethylenes (HDPEs) influences the environmental stress crack resistance. Polymer samples were characterized in terms of their semicrystalline microstructure. A certain stereoregularity was identified for the copolymer fraction, and a linear correlation between the stress crack resistance, which was assessed by the full notch creep test, and the fraction of stereoregular chains in the HDPE was established. Conceptual models to understand the action of the stereoregular copolymer chain in the slow crack growth mechanism are proposed. The results found in the present research will serve as guidelines for tailoring the properties of bimodal high-density polyethylene through optimization of the operating parameters of the reactors and catalyst design.