Strain hardening has important roles in polymer processing such as foaming, film forming, and fiber extruding. A common method to enhance this behavior is chemically branching the backbone of polymers, which is costly as well as discouraging the users from controlling the degree of the behavior. We have developed a new fiber reinforcement technology to solve these issues. Our previous study showed that the technology of blending smart microfibers would be able to tune the degree of strain hardening more cost efficiently. In this study, we fabricated the fibers in a nano-scale. These smart nanofibers can induce controlled pre-stressing in the matrix by responding to external stimuli such as temperature variation. We have chosen two polymers with a difference in melting temperatures large enough to characterize and process when the matrix is molten and the fibers are not, therefore, retaining the fiber structure and having a sufficient temperature window to study the possibility of tailoring the strain hardening. Rheological measurements show that blending with in-situ shrinking nanofibers enhances strain hardening significantly compared to that of non-shrinking nanofibers. Extrusion foaming results also show that blending with in-situ shrinking nanofibers improves the foamability significantly.