The structural organization of blends of isotactic polypropylene (iPP) and linear low-density polyethylene (LLDPE), with different compositions, was studied and correlated with the thermal history followed by the samples during solidification from the molten state. The materials were cooled at two extreme controlled rates: 0.1 and 500 degreesC/s. The resulting structure was investigated both in the crystalline and the amorphous phases. In particular, attention was focused toward the analysis of the diffusion parameters of dichloromethane vapors, and the morphological organization of the amorphous phases was interpreted using models that consider them (in terms of resistance to diffusion) combined in series and in parallel.