Modern architectural designs demand materials that are both aesthetically flexible and functionally lightweight and durable. To address this need, white cement-based, 3D textile-reinforced composites with waterproof membranes were developed. The aim was to produce structural elements that are flexible, lightweight, water-resistant, and capable of retaining complex shapes. During fabrication, 3D textile pieces were placed into wooden molds, filled with white cement, and a waterproof membrane was applied to the surface. The specimens were tested for unit weight, flexural, and tensile properties at 7 and 28 days. The results demonstrated that the composites exhibited remarkably low unit weights ranging from 0.77 to 0.83 kg/dm³, high flexural strength of up to 16.32 MPa, and tensile elongation exceeding 30%. While initial crumbling of the cement matrix was observed during tensile testing, the textile reinforcement effectively preserved specimen integrity, limited crack propagation, and enhanced energy absorption. Consistent performance under both static and dynamic loading confirmed the material’s ductility, shape adaptability, and robustness. These findings suggest that the composite is particularly suitable for architectural components requiring freeform geometries, flexibility, and portability. Additionally, its lightweight and water-resistant properties provide significant advantages for temporary or movable structures, as well as for integration with novel fabrication techniques such as 3D printing and modular construction systems.