Metallic effect in injection molded parts is created using composites of high-density polyethylene (HDPE) filled with high-sparkle aluminum (Al) pigments (HDPE/Al). The mechanism of micro shrinkage induced by the leafing phenomenon influences the surface topography and roughness, and has been studied with SEM and AFM. Reflectance, whiteness index (WI), and luminance (L*) of the surface were assessed in relation to the surface roughness, the particle sizes, the crystallinity and thermal conductivity of composites. The results show that the leafing induces the micro shrinkage and causes micro caverns, which increased surface roughness. Besides, the length of micro caverns and surface roughness increased as the particle size increased. These morphologies were not benefit for improving reflectance, WI, and L* values, therefore the reflectance, WI, and L* values decreased proportionally with the surface roughness and particle sizes increased. High-sparkle Al pigments improved the crystallinity and thermal conductivity of the composites. A higher reflectance, WI, and L* were associated with a higher crystallinity and a higher thermal conductivity. POLYM. ENG. SCI., 2017. (c) 2017 Society of Plastics Engineers