The blends of very high molecular weight high-density polyethylene (VHMW-HDPE) or ultrahigh molecular weight high-density polyethylene (UHMW-HDPE) and low-density polyethylene with normal molecular weight (LDPE) in equal or prevailing concentrations of the first component have excellent mechanical properties but very high viscosity in a molten state. The present investigations are a continuation of the fact, established by us for the first time, that the addition of a third polymer, isotactic polypropylene (I-PP), at optimal low concentrations increases the melt flowability of these systems without considerable deterioration of their very good mechanical properties in the solid semicrystalline state. The comparison between the thermomechanical behavior and the sorption in organic media of the systems leads to the supposition that an uninterrupted physical network from the VHMW-HDPE has been formed.