Recent developments in materials and processes for additive manufacturing (AM) have moved 3D printing beyond just prototyping of manufactured parts and into exciting new applications. For example, various researchers and industries have successfully demonstrated the use of conductive filler modification in materials for use with fused deposition modeling (FDM)-based 3D printers. Due to the piezoresistive effect, these conductive filler-modified materials can be used to print highly customizable sensors on-demand. This is notable because combined with the versatility of FDM printing, it allows for a completely new interpretation of what a sensor is and what a sensor should look like. The accuracy and reliability of these sensors is still under investigation, and common AM materials such as polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS) have been the subject of most investigations. Thermoplastic polyurethane (TPU), a commercially available flexible filament, has been less studied for conductive filler modification and printed sensors. This is an important gap in the state of the art because flexible sensors are becoming increasingly important in applications involving large deformations such as soft robotics. Therefore, this work presents the results of an initial study on the development of a carbon nanofiber (CNF)-modified TPU for the development of flexible piezoresistive-based printed sensors. Specifically, this work considers the effect of different manufacturing parameters on CNF/TPU conductivity and printability using a commercially available FDM printer. Ultimately, this project seeks to utilize the proposed functionalized TPU material for the production of embedded sensors in rigid or flexible 3D printed parts.