Phase-change materials (PCMs) are a useful alternative to more traditional methods of thermal management of various applications. PCMs are materials that absorb large amounts of latent heat and undergo solid-to-liquid phase change at near-constant temperature. The goal of the research is to experimentally investigate the thermal properties of a novel shape-stabilized PCM/HDPE composite extruded filament. The extruded filament can then be used in a 3D printer for custom PCM/HDPE shapes. The PCM used in the study is PureTemp PCM 42, which is an organic-based material that melts around 42 °C. Four PCM/HDPE mixtures were investigated (all percentages by mass): 20/80, 30/70, 40/60, and 50/50. Preliminary findings include differential scanning calorimeter (DSC) measurements of melting temperature and latent heat as well as scanning electron microscope (SEM) pictures of filament composition.