Solution processable polymers that can reproducibly form metal filament by applying voltage are investigated for nonvolatile memory application. Up to present, the understanding of materials enabling to make the metal filament has not been well-documented and the vacuum deposition methods were dominantly used in device fabrication. After screening various polymers, we found that only the polymers having two functionalities, the presence of strongly coordinating heteroatom (S or N) with metal ions and the electrical conductivity, showed the reproducible filament formation behavior. Among the polymers screened, the regiorandom poly-(3-hexylthiophene) showed the best switching endurance over 30 000 write-read-erase-read cycles without any switching failure.