As additive manufacturing (AM) increasingly gains commercial and academic interest, government agencies, such as NASA Johnson Space Center, seek to produce thermal protection systems using AM methods, such as fused filament fabrication (FFF). The purpose of this study is to develop a suitable polyetherimide (ULTEM (TM) 1010) nanocomposite with enhanced ablation and thermal properties while maintaining compatibility with commercially available FFF machines. Eleven formulations were compounded using the twin-screw extruder with varying amounts of nanoclay, glass bubbles, and flame-retardant additives. All formulations were characterized via multiple instruments to be down-selected to four candidates for aerothermal testing. After discovering specific characteristics of some formulations, aerothermal test models were 3D printed for four formulations. Enhanced thermal properties among the composite formulations were demonstrated. Aerothermal testing also displayed promising results. In addition to experimental data, microstructural analyses were performed.