Two different samples of high-density polyethylene (HDPE) were studied. One (isotropic) was extracted from the material core, whereas the other (anisotropic) involved two sides that were in contact with the injection mold. Using radiofrequency field gradients, it was observed by NMR microscopy that these two sides favor toluene penetration into the material. Solvent diffusion in both samples could be successfully modeled, as demonstrated by the comparison between experimental NMR images and simulated images. Weight measurements appear to be consistent with the quantitative conclusions derived from NMR microscopy data.