Longwave-transparent low-emissivity material

Low-emissivity (low-e) materials are crucial for conserving thermal energy in buildings, cold chain logistics, and transportation by minimizing unwanted radiative heat loss or gain. However, their metallic nature intrinsically causes severe longwave attenuation, hindering their broad applications. Here, we introduce an all-dielectric longwave-transparent low-e material (LLM) with ultra-broadband, high transmittance spanning nine orders of magnitude, from terahertz to kilohertz frequencies. This meter-scale LLM not only achieves energy savings of up to 41.1% over commercial white paint and 10.2% over traditional low-e materials but also unlocks various previously unattainable capabilities including high-speed wireless communication in energy-efficient buildings, wireless energy transfer with radiative thermal insulation, as well as noninvasive terahertz security screening and radio frequency identification in cold chain logistics. Our approach represents a photonic solution toward carbon neutrality and smart city development, paving the way for a more sustainable and interconnected future.