Linear and nonlinear viscoelastic properties for binary blends composed of isotactic polypropylene and polytetrafluoroethylene (PTFE) are studied. It is found that blending a small amount of PTFE greatly enhances the storage modulus in the low frequency region. Further, drawdown force and normal stress difference increase with the PTFE content. Electron microscope observation reveals that PTFE deforms into fine fibers whose diameter is smaller than 0.5 mu m. The network structure composed of the fibers is responsible for the marked elastic properties. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2008-2014, 2009