A facile approach to achieve subambient radiative cooling through aluminum foils and polyethylene bubble wrap

Subambient radiative cooling is an emerging passive cooling strategy that simultaneously reflects the incident solar irradiance to depress the heat gain and radiates heat from objects to enhance the heat loss without any electricity consumption from compressor-based air-conditioning. Although numerous efforts have been dedicated to developing materials, such as complicated photonic crystals and metamaterials or expensive polymer composites with both high solar reflectance and infrared emittance, the gap still exists between efficient radiative cooling performance and an affordable radiative cooling device. Here, a facile, low-cost, and home-built approach to achieve efficient subambient radiative cooling, which employs commercially available materials of the polyethylene (PE) bubble wrap and aluminum foils, is reported for scalable industrial and domestic applications. The aluminum foils are infrared-reflective and sunlight-opaque, acting as a solar shield and infrared waveguide, which can both block the solar irradiation and guide infrared thermal radiation to the cold outer space. PE thin film is infrared-transparent with a high mid-infrared transmittance that allows mid-infrared thermal radiation to pass through. It is thermally insulating with a low thermal conductivity of 0.038 W/m ⋅ K after being fabricated into air-filled bubbles to minimize parasitic non-radiative heat transfer. An average subambient temperature reduction of 4.0°C has been achieved during the noontime in summer. These commercially available materials make this design a practical technique for people to realize an affordable and comfortable interior environment during the summer in a cost-effective manner without any professional constructions. The nature of low-cost, home-built, and easily integrated into buildings renders it attractive for everyone, especially for those in developing regions.