Thermal and mechanical insights into sandwich structures: A comparison of XPS foam and Prisma composite cores

Buildings are responsible for approximately 40% of global energy consumption and 30% of carbon dioxide (CO₂) emissions, with a significant portion of this energy dedicated to maintaining thermal comfort. Retrofitting existing buildings with sandwich panels offers a practical solution to reduce thermal loads and, consequently, energy consumption. In this study, sandwich structures composed of glass fiber reinforced polymer (GFRP) skins and polymeric foam cores were fabricated using the vacuum assisted resin transfer molding (VARTM) process. Two core materials, extruded polystyrene (XPS) foam and polyurethane (PU) foam integrated within Prisma beams, were evaluated through thermal and mechanical testing. The panels achieved thermal resistances ranging from 3.62 to 4.66 h.ft². °F/Btu (0.64-0.82 K.m²/W) per inch. Under quasi-static loading, XPS samples exhibited 24%–40% higher strength and 16%–28% greater brittleness compared to PU. In low-velocity impact (LVI) tests, PU cores absorbed 11% more energy than XPS. However, flatwise tensile testing showed that the bonding strength between XPS and GFRP was 47% higher than that of PU. Overall, the findings indicate that XPS is the more effective core material for sandwich panel retrofits, offering superior thermal insulation and mechanical performance.