Rigid Expanded Polystyrene (EPS) insulation is widely used in construction for its thermal performance, but its mechanical property—compression strength—is equally critical for many structural applications. Compression strength refers to the ability of EPS foam to withstand compressive loads without significant deformation or failure. This property is directly tied to the density of the material. Typically, standard EPS insulation has a density ranging from 15 kg/m³ to 35 kg/m³. At a common density of 20 kg/m³, the compression strength is approximately 100 kPa, while denser boards (30 kg/m³) can achieve values over 150 kPa. However, high-load industrial applications such as insulated concrete slabs, green roofs, and heavy-traffic floors require EPS with a density of 40 kg/m³ or more, delivering compression strengths up to 300 kPa. The test method for EPS compression strength follows standardized procedures, usually ASTM D1621 or ISO 844, where a specimen is compressed at a constant rate until a 10% strain is reached. This value defines the compressive resistance. Importantly, EPS is a closed-cell foam, and its strength comes from the cell wall structure rather than the air inside. When loaded, the cells collapse gradually, absorbing energy without a sudden brittle failure. This makes EPS a reliable cushioning and insulation material in sandwich panels for cold storage and structural insulated panels (SIPs). For load-bearing applications, engineers evaluate both short-term and long-term creep behavior. Over time, continuous static loads can cause deformation even below the rated strength. Therefore, design values typically use a safety factor of 1.5 to 2.0. Users must also consider temperature effects; at higher temperatures, EPS softens, reducing compression capacity. In summary, the compression strength of rigid EPS insulation is a function of density, quality control, and environmental conditions. Selecting the correct grade ensures both thermal efficiency and structural safety. For residential floors, 100-150 kPa is typical; for heavy refrigeration warehouses, 200-250 kPa is recommended. Always check manufacturer data sheets and perform project-specific structural analysis before specifying EPS insulation for load-bearing roles.