This chapter presents a suitability analysis of 3D-printed cellulose-based polymeric materials for electrical insulation applications. Polylactic acid (PLA) and nanocrystalline cellulose (NCC) bionanocomposites were produced, and their multiphysical, dielectric, and mechanical properties were analyzed. The addition of nanofillers increased the mechanical properties of the bionanocomposites through reinforcement effects and the increased crystallinity due to nanofiller nucleation. The nanofiller incorporation, however, slightly reduced the electrical insulation properties by increasing the dielectric constant, dielectric loss, and electrical conductivity of 3D-printed bionanocomposites. This effect was associated with the polarity of the nanofillers, as demonstrated by chemical surface analysis. By adjusting the sample architectures, we have rendered the dielectric and mechanical properties of NCC-based bionanocomposites competitive with synthetic polymers used in electrical insulation, such as LDPE, HDPE, PP, and PVC. A final 5-month aging stage in water and at room temperature showed that, despite the increased polarity of the bionanocomposites due to the addition of NCCs, the nanofiller had very little effect on water absorption and consequently little effect on long-term electrical insulation performance. This investigation will provide insights into the design of bio-based materials for long-term electrical insulation applications.