We synthesized CuS and Cu1.8S nanoparticles with localized surface plasmon resonance absorbance in the near-infrared region and applied a silica layer to enhance their photo-stability and dispersion stability. These plasmonic Cu2−xS nanoparticles are effective thermal shielding materials for energy-saving windows, blocking UV and NIR regions while transmitting visible light. The silica coating suppressed photocatalytic activity and improved the dispersion in polymer films, making them reliable thermal shielding materials. A simulated experiment showed that CuS/SiO2–PDMS films had a smaller temperature change (ΔT = 6.8 °C) compared to common glass (ΔT = 12.7 °C) and CuS–PDMS films (ΔT = 9.2 °C).