Like many sectors across the European Union, the gypsum industry is actively seeking strategies to reduce its environmental footprint by lowering product density while maintaining quality and performance standards. To address this, a resource-efficient strategy that reduces gypsum and water consumption, and thereby lowering energy use without sacrificing mechanical performance is pursued. In this study we establish the relationship between the three-dimensional characteristics of air voids such as volume fraction, size distribution, sphericity, polydispersity, packing density, and tortuosity within the gypsum matrix and the resulting mechanical performance of the material. Standard and advanced characterization techniques, such as mercury intrusion porosimetry (MIP), X-ray micro-computed tomography (μCT), and mechanical testing were used to investigate the gypsum core structure and its mechanical properties. These characterizations served as a benchmark for quantifying the relationship between pore structure and material properties in gypsum plaster. Additionally, a straightforward methodology was developed to produce model porous samples with controlled porosity parameters using polystyrene (PS) beads. These polystyrene beads of known diameter were added in the gypsum plaster paste and mechanical tests were carried out. The samples were compared with identical counterparts from which polystyrene had been leached out. The results indicate that polystyrene can effectively serve as a surrogate for air voids in representing porosity within the gypsum matrix.