The roof stability of artificial structures constructed by cementitious tailings backfill (CTB) is one of the major aspects in the durability of underhand cut and fill mining method. This is because CTB's failure can threaten worker and equipment safety and create ore dilution. An interesting question is whether 3D printed polymeric lattice (3DPPL) can enhance powerfully CTB's strength characteristics? To explore this topic, diverse 3DPPL shapes (i.e., hexagon, square and rhombus) and material types (i.e., transparent resin TR, nylon NY and ordinary resin OR) were considered. Three-point bending tests on CTB samples were carried out with scanning electron microscopy observations to measure their flexural and microstructural characteristics. The following inferences showed that U-shaped 3DPPL reinforced CTB significantly offered improved flexural strengths when material types were OR and NY. However, material type TR presented a major weakening influence on CTB's flexural strength. For a given CTB recipe, rhombus and OR were selected as the best polymer shape and material type among others. All U-shaped 3DPPL reinforced backfills better flexural deflection values than N-3DPPL reinforced ones. The maximum and minimum reinforcement multiples were 44.9 and 0.9. U-shaped 3DPPL obviously changes CTB's flexural characteristics, from traditional brittle failure to ductile failure. The outcomes of this work can afford a strong source for popularization and implementation of underhand cut-and-fill mining system and the stability control of the backfilling materials.