This chapter highlights the fabrication of polyurethane (PU) composite structures using 3D printing that involves purification, dehumidification and mixing processes in the preparation step. Purification and dehumidification aim to remove the impurities and minimise the moisture content of PU and PU composites. Meanwhile, the mixing process, consisting of solution mixing, melt mixing and the combination of both methods, is implemented to obtain a homogeneous mixture. The mixture acts as feedstock materials that are processed by 3D printing to produce PU composite samples. Those samples are then tested to determine their mechanical, thermal and electrical properties.