Experimental Evaluation of Advanced Reflective TiO2-Based Coatings for Passive Cooling of Building Envelope Materials

Space cooling is one of the fastest-growing end uses in the building sector, and reflective (“cool”) coatings have emerged as a low-cost passive strategy to limit solar heat gain through the envelope. This study evaluates the summer thermal behaviour of three building-envelope materials commonly used in flat roofing—self-protected asphalt sheet, steel sheet, and ceramic tile—under outdoor conditions in Valencia, Spain. Sealed cubic prototypes were monitored to compare uncoated reference specimens with specimens coated with a conventional high-performance white acrylic paint produced by SOETAM and with an advanced reflective coating based on a laminar TiO2 nanostructure produced by Q+TERMIK. External surface temperatures were assessed by infrared thermography and internal air temperatures by autonomous data loggers. External white coatings significantly reduced surface temperatures across all substrates, with the effect most pronounced in low-thermal-inertia materials: the advanced reflective coating achieved peak surface-temperature reductions of 21.0 °C (33.2%) for asphalt and 17.4 °C (28.8%) for steel, outperforming the high-performance coating, with corresponding internal reductions of up to 9.7 °C (22.0%) and 8.1 °C (18.6%). The results indicate that the advanced reflective coating produced greater thermal mitigation than the conventional coating under the tested outdoor conditions, despite both coatings being applied with similar thicknesses. The advanced reflective coating generally produced the greatest thermal mitigation, particularly for low-thermal-inertia substrates, while the ceramic tile exhibited a different internal thermal response, highlighting the influence of substrate properties on coating performance.