ABSTRACT In this work, the interplay effects of hollow glass bead (HGB) contents and uniaxial stretching ratios on HGB filled bimodal polypropylene (PP) films were studied. Stretching was carried out at about 120˚C relatively near to the crystallization temperature of PP. The porous PP films’ surfaces were analyzed using a scanning electron microscope (SEM). SEM micrographs showed that the pore sizes and numbers could be controlled by the filler contents as well as stretching ratios. It was also observed that the porosity and permeability of the films increased with increasing HGB content, however at high loadings, they decreased with the increase in stretching ratio. The yielding behavior of the precursor and porous PP samples prepared by hot stretching was analyzed by tensile testing. The results revealed that with the increase of the number of pores, strain softening was faded and eventually completely removed. Therefore, a ductile-brittle transition occurred in the behavior of the polymer. The crystallinity of the precursor PP films was also increased with the increase in filler content. In addition, the melting temperature was decreased and the crystallization temperature was increased. An additional melting peak was appeared below the main melting temperature by incorporating the particles in porous films compared to those in precursor films. KEYWORDS: Polypropylene (PP); Hollow glass bead; Porous films; Stretching ratio; Permeability. Corresponding Author: Jalil Morshedian (J.Morshedian@ippi.ac.ir)