By reducing tensile test speeds over four orders of magnitude, from 5 to 0.001 mm/min (corresponding to the initial strain rate of 4 × 10−3 to 8 × 10−7 s−1), color of polyethylene (PE) specimens remains translucent during the necking process, no longer changing to opaque white. Since changing the color to opaque white indicates the presence of cavities, the unchanged color suggests that such cavitation process is avoided by reducing the crosshead speed. With this discovery, the study proceeds to investigate the mechanical behavior of PE specimen shown at two crosshead speeds, 1 and 0.001 mm/min, before neck is developed; the former crosshead speed leads to opaque white neck but the latter translucent. The results show that at 1 mm/min, a stretch corresponding to a strain smaller than 4% can cause degradation of mechanical properties. Since this level of deformation is close to that allowed in service, the study recommends the consideration of in-service loading rate for evaluation of the mechanical properties, especially for long-term applications such as plastic pipes for natural gas transportation. POLYM. ENG. SCI., 54:1871–1878, 2014. © 2013 Society of Plastics Engineers