High-Reflectance Low-Emissivity Multilayer Wallpaper for Envelope Cooling and Energy Saving of Tropical Buildings

Buildings account for a large share of global energy use, and tropical cooling loads are intensified by solar radiation and humidity. This study characterizes a tape-applied four-layer wallpaper (PET grid fabric/PVC/commercial aluminized film/PE) on one model house per finish in Hainan, China. Laboratory solar reflectance is approximately 0.77 and comparative 8–13 µm emissivity is 0.32–0.38, indicating a solar reflector plus radiant barrier rather than a high-emittance sky-window cooler. In May 2022, EE-1 reduced exterior-roof and indoor-air temperatures by up to 8 °C and 4 °C relative to a contemporaneous uncoated house. Treatments were not randomized, and no pre-treatment baseline exists, so the contrasts are descriptive. Electricity use was 10% and 22% lower at 23 and 20 °C; the 2% contrast at 26 °C is not primary evidence. After 3–4 months, EE-1 delaminated. Retrieved EE-1 retained solar reflectance of 0.769, while transverse elongation fell to 58% of the unexposed value. EE-3/EE-4 improved short-term appearance only. Cooling and multi-month durability were not demonstrated for one formulation.