Locally anisotropic porous materials were prepared using linear low-density polyethylene (LLDPE) and crystallizable organic diluents by thermally induced phase separation processes. Pyrene and hexamethylbenzene (HMB) were selected as crystallizable diluents because of their miscibility with LLDPE at elevated temperature, higher crystallization temperatures than that of LLDPE, and their individual (very different) crystallization behaviors. Equilibrium phase diagrams were calculated using the Flory-Huggins theory of solution thermodynamics and show good agreement with experimental observations. The phase separation process, which was monitored visually using an optical microscope equipped with a temperature controller, shows strong dependence on solution composition as well as the diluent identity. Solidified materials after extraction of pyrene from pyrene/LLDPE mixtures exhibit locally aligned layers of pores, with features that depend on solution composition. The pores inside semicrystalline polyethylene domains are aligned in the crystal growth direction of pyrene, which crystallizes before LLDPE upon cooling, When HMB is the crystallizable diluent, platelike pore structures, much larger in size than the pyrene-derived pores, are observed, consistent with reports of other investigators. These observations arc discussed in terms of the phase transformation processes caused by the different crystallization behavior of the diluents.