The tensile impact performance of polymer/polymer microlayer composites (PPC) was studied before and after storage in unleaded fuel at an ambient temperature (RT) and at -40 degrees C, respectively. The PPCs were produced by extrusion blow molding of high-density polyethylene (HDPE), d = 0.945 g/cm(3), blended with a modified polyamide (Selar(TM) RB 901 of DuPont) in 4, 7, and 14 wt %, respectively. It was shown that the fuel absorption obeys the Fickian law of diffusion. With increasing Selar content the sorption was reduced, whereas diffusion (D) and permeability (P) coefficients of the PPCs did not appear to change. The Selar microlayers worked as reinforcements, so that the strength and stiffness of the PPCs were increased, however, at the cost of the ductility and toughness. The exact opposite trends were observed due to fuel absorption. Gasoline, acting as plasticizer, resulted in reduced stiffness and strength with simultaneously increased ductility and toughness of the PPCs. All of the above-mentioned properties were similar for all blends after storage in gasoline. The failure mechanism of the PPCs was studied by fractography and is discussed in relation to the composite structure.