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PE100 features excellent creep and slow crack resistance (SCG). It is common to add color masterbatch to the natural PE100 material to produce compound ready for pipe extrusion. The polyethylene base of the masterbatch is not usually PE100 and therefore can harm the creep and SCG resistance of the PE100. In this paper the effects of small contents of a linear low-density polyethylene (LLDPE) and a unimodal high-density polyethylene (uni-HDPE) on the physical and mechanical properties, specifically strain hardening modulus (SHM) and SCG resistance of a pipe grade bimodal high-density polyethylene (bi-HDPE, PE100) were investigated. Varying contents of 0, 2.5, 5, and 10 wt% of the LLDPE or uni-HDPE were blended with the bi-HDPE in either a lab single screw extruder or internal mixer to compare the effects of the mixing method. Strain hardening test, notched constant tensile load (NCTL) test, Pennsylvania notched test (PENT) were employed to study the SCG resistance. Tensile test, melt flow index (MFI), rheological measurements, scanning electron microscopy (SEM) were also used for characterizing the samples. The results showed that the addition of 2.5 and 5 wt% of LLDPE or uni-HDPE had no significant influence on the strain hardening modulus of bi-HDPE while adding 10 wt% of LLDPE or uni-HDPE resulted in 4.3 to 12.2% reduction in SHM. The blends prepared with the single screw extruder showed more deterioration in the SHM values of the final blends compared to those prepared in the internal mixer. NCTL and PENT confirmed the trend of SHM results. [ABSTRACT FROM AUTHOR]