How much cooling can passive radiative cooling really deliver?
The best passive radiative cooling materials now achieve temperature reductions that rival or exceed conventional cooling in sunny, dry conditions. A 2024 metasurface emitter set a record by cooling 15.4°C below ambient under strong sunlight (~800 W/m²) [6]. Another advanced emitter from the same year reached an average sub-ambient drop of 20.1°C with a cooling power of 121 W/m² [10]. These are not just lab curiosities — a ceramic nanofibrous aerogel kept a box 18.6°C cooler than the outside air under sunlight [5]. For context, a typical window air conditioner might cool a room by 10–15°C, so these passive materials are in the same ballpark for the object itself.
Performance drops in humid or cloudy conditions, but remains useful. A microporous glass coating still achieved 3.5°C daytime and 4°C nighttime cooling even at 80% humidity [1]. That is less dramatic than the 15–20°C drops, but still enough to reduce air-conditioning load significantly.
Can it replace air conditioning or cooling textiles in practice?
For personal textiles, the answer is clearly yes — and the performance is impressive. A hierarchical metafabric cooled simulated skin by 16.6°C compared to traditional textiles, with about half of that coming from moisture-wicking [4]. Another metafabric achieved 13.8°C cooling in dry conditions and 19.3°C when sweating, and was estimated to save ~19.3% of annual building HVAC energy in Shanghai [2]. A large-scale woven metafabric, produced via industrial textile methods, cooled a human body by ~4.8°C compared to cotton fabric [8]. These are not just incremental improvements — they represent a genuine alternative to active cooling for personal comfort.
For buildings, the picture is more nuanced. The cooling glass coating [1] and ceramic aerogels [5] are durable and weather-resistant, but they work best as a supplement to, not a replacement for, HVAC. The 19.3% energy savings estimate [2] is significant but assumes integration with existing systems. A switchable coating that can toggle between cooling and heating modes [7] addresses the seasonal limitation — it reflects 96.6% of sunlight when dry (cooling) and transmits 86.6% when wet (heating) — making it viable for climates with large daily temperature swings.
What are the practical barriers and trade-offs?
Cost and scalability are the main hurdles, but progress is rapid. The oyster-shell-derived film [3] and transparent wood coating [11] show that low-cost, sustainable materials can work — the oyster-shell film reached 7°C sub-ambient cooling using waste calcium carbonate. The metafabrics [2][4][8] are produced via electrospinning or industrial weaving, which are already scalable. The ceramic aerogel [5] withstands 830°C and passes environmental aging tests, suggesting long-term durability.
Performance is highly dependent on sky conditions. All materials rely on emitting heat through the atmospheric window (8–13 µm) into space, which works best on clear nights. During overcast days or in humid climates, cooling power drops. The metafabric that achieved 19.3°C cooling in sweating conditions [2] also shows that integrating sweat evaporation can compensate for reduced radiative performance. No single material works optimally everywhere — the best choice depends on local climate, application (textile vs. building vs. electronics), and cost constraints.
About These Sources
This answer is built on 11 peer-reviewed studies — published from 2021 to 2025, 6 from 2024 or later, 11 in Q1 journals, collectively cited 2,029 times — selected as the most relevant from 12 studies that passed quality screening, drawn from 56 papers retrieved from a database of over 500 million.
Sources used in this answer
A solution-processed radiative cooling glass
A microporous glass coating achieved 3.5°C daytime and 4°C nighttime sub-ambient cooling even at 80% humidity, and remained stable under water, UV, soiling, and high temperatures.
A High‐Performance Passive Radiative Cooling Metafabric with Janus Wettability and Thermal Conduction
A hierarchical metafabric with 99.7% solar reflectivity and 92.4% infrared emissivity cooled 13.8°C (dry) and 19.3°C (sweating) under sun, and was estimated to save ~19.3% annual building HVAC energy in Shanghai.
Turning Discarded Oyster Shells into Sustainable Passive Radiative Cooling Films
A film made from discarded oyster shells (CaCO₃) and polyurethane achieved 7°C sub-ambient cooling under 650 W/m² solar irradiance, outperforming white paint and pure PU.
A Moisture-Wicking Passive Radiative Cooling Hierarchical Metafabric
A moisture-wicking nanofiber metafabric cooled simulated skin by 16.6°C vs. traditional textiles, with ~8.2°C from humidity management alone.
Hierarchical Ceramic Nanofibrous Aerogels for Universal Passive Radiative Cooling
A ceramic nanofibrous aerogel achieved 98.1% solar reflectance and 92.1% atmospheric-window emissivity, with a theoretical daytime cooling power of 103.3 W/m²; a covered box averaged 18.6°C sub-ambient cooling under sunlight.
Ultrahigh performance passive radiative cooling by hybrid polar dielectric metasurface thermal emitters
A machine-learning-designed metasurface emitter achieved ~0.92 emissivity in the 8–13 µm window, a spectral selectivity of ~1.8, and a record 15.4°C sub-ambient cooling under ~800 W/m² solar irradiation.
Switchable Surface Coating for Bifunctional Passive Radiative Cooling and Solar Heating
A switchable coating with hierarchical pores achieved 96.6% solar reflection (dry, cooling mode) and 86.6% solar transmission (wet, heating mode), enabling all-day near/sub-ambient cooling in tropical climates.
Hierarchical-morphology metafabric for scalable passive daytime radiative cooling
A large-scale woven metafabric with 94.5% atmospheric-window emissivity and 92.4% solar reflectivity cooled a human body ~4.8°C below cotton fabric, and was produced via industrial textile routes.
Passive Radiative Cooling Enables Improved Performance in Wearable Thermoelectric Generators
A wearable thermoelectric generator with a radiative cooling coating achieved ~128% higher output power outdoors and ~96% higher indoors compared to the pristine device.
An advanced passive radiative cooling emitter with ultrahigh sub-ambient cooling performance
An advanced passive radiative cooling emitter with 95.5% reflectance and 97.9% emissivity achieved an average 20.1°C sub-ambient temperature drop and 121.0 W/m² cooling power under intense sunlight.
Transparent Wood for Passive Radiative Cooling of Solar Absorbers
Transparent wood coatings functionalized with ZnO nanoparticles showed ~0.95 mid-infrared emissivity and lowered silicon substrate temperature by ~6–7°C under direct sunlight.