Passive Radiative Cooling Technologies and Materials

Passive radiative cooling exploits the natural ability of surfaces to emit thermal radiation into the cold sink of outer space through the atmospheric transparency window, typically between 8 and 13 µm. By engineering materials with high emissivity in this infrared band while simultaneously reflecting incoming solar radiation, surface temperatures can fall below ambient without any energy input. Recent advances encompass nanophotonic structures, polymer films with hierarchical porosity, metasurfaces and adaptive systems based on phase-change materials. These approaches deliver sub-ambient cooling for buildings, electronic devices, solar cells and personal thermal management. Materials range from low-cost roll-to-roll processed polymers to complex multilayer dielectric stacks and selective thermal emitters. The interplay of spectral selectivity, angle-dependent emissivity and durability under real-world conditions defines performance. Beyond energy savings in air-conditioning and refrigeration, passive radiative cooling offers pathways to mitigate urban heat island effects, improve photovoltaic efficiency and enable novel wearable thermal-management textiles.

Research from Nature Portfolio

A hierarchically structured polymethyl methacrylate film incorporating micropores and nanopores has demonstrated all-day cooling performance with solar reflectance above 0.95 and long-wave infrared emittance near 0.98, achieving average sub-ambient temperature reductions of around 6–9 °C under typical midday sunlight. A selective thermal emitter design has achieved ultra-large temperature reductions of up to 42 °C below ambient through elimination of parasitic heat loads, sustaining a mean 37 °C drop over a full diurnal cycle in clear-sky conditions. A dual-mode device with electrostatically controlled contact conductance integrates passive radiative cooling with solar heating, yielding up to 72 W m⁻² of cooling power and 643 W m⁻² of heating power, with building simulations indicating nearly 20 % savings in annual heating and cooling energy.

Passive Radiative Cooling Technologies and Materials publication trend

The graph below shows the total number of articles in passive radiative cooling technologies and materials across all publications each year (not limited to Nature Index journals).

Technical terms

Passive radiative cooling: The process by which a surface loses heat by emitting infrared radiation to outer space without external energy input.

Atmospheric transparency window: A spectral band (8–13 µm) in which Earth’s atmosphere is largely transparent, allowing thermal radiation to escape to space.

Emissivity: The efficiency with which a material emits thermal radiation at a given wavelength relative to an ideal blackbody.

Solar reflectance: The fraction of incident solar radiation that a surface reflects rather than absorbs.

Spectral selectivity: The property of a material or structure to exhibit different emissivity or reflectance at different wavelengths.

Phase-change materials: Substances that undergo reversible transitions (e.g. metal-insulator) with temperature, enabling adaptive control of radiative properties.

References

1. A structural polymer for highly efficient all-day passive radiative cooling. Nature Communications (2021).
2. Radiative cooling to deep sub-freezing temperatures through a 24-h day–night cycle. Nature Communications (2016).
3. Integration of daytime radiative cooling and solar heating for year-round energy saving in buildings. Nature Communications (2020).
4. Highly efficient flexible structured metasurface by roll-to-roll printing for diurnal radiative cooling. eLight (2023).
5. Self-adaptive radiative cooling based on phase change materials.. Optics Express (2018).
6. Radiative cooling of solar cells. Optica (2014).