When ultra-high-molecular-weight polyethylene (UHMWPE) in powder form is injection molded, the so-called delamination layering occurs near the skin of the parts. This layering defect hampers UHMWPE's superior wear resistance property and part surface quality. The delamination layer was caused by a combination of excessive shear stress near the part surface and high degree of molecular entanglement of UHMWPE. A mold insulation method that delays the rapid cooling of UHMWPE to reduce the shear stress and improve the polymer chain "interdiffusion" across the entangled chain bundles was used to eliminate the delamination layer. When the insulation layer thickness and mold temperature were optimized, the delamination layer was eliminated completely while still maintaining a reasonable cooling/cycle time. The delamination-free parts were found to regain UHMWPE's superior impact resistance and tensile properties. POLYM. ENG. SCI., 59:2313-2322, 2019. (c) 2019 Society of Plastics Engineers