We propose a microscopic structural deformation model of hard elastic polypropylene (HEPP) during uniaxial stretching using time-resolved simultaneous wide-and small-angle X-ray scattering measurements. It is found that 'double' yielding point, characteristic of HEPP in the tensile deformation, corresponds to the formation of the voids with a fine chain slip within the lamellae, followed by the fragmentation of the lamellae associated with a coarse chain slip. Based on the X-ray scattering measurements, we discuss relationship between the strain in the cold stretching and air permeability of a microporous membrane prepared by hot stretching, following the cold stretching. (C) 2015 Elsevier Ltd. All rights reserved.