How does passive radiative cooling work, and why is it suited for lower-resource settings?
Passive radiative cooling (PRC) works by reflecting sunlight and emitting heat as infrared radiation through the atmosphere into outer space, requiring no electricity. This makes it ideal for off-grid or energy-poor regions where conventional air conditioning is unavailable or unaffordable. For example, a microporous glass coating achieved a temperature drop of ~3.5°C during midday and ~4°C at night, even in high humidity [1], while a fabric treated with a metal-organic framework (MOF) called UiO-66(Zr) lowered temperatures by up to 5°C [3]. These materials can be applied to roofs, walls, or even clothing, directly reducing heat stress without power.
What are the practical barriers to deploying PRC in lower-resource settings, and how are they being addressed?
Key barriers include cost, durability, and the need for reliable performance testing. Many PRC materials use complex nanostructures that are expensive to produce, but scalable alternatives exist: a microporous glass coating is made from abundant materials and withstands water, UV radiation, and high temperatures [1], and a woven metafabric produced via industrial textile routes is cost-effective, waterproof, and breathable [7]. Another challenge is that PRC performance drops under cloudy or humid conditions, but a dual-mode asymmetric photonic mirror can switch between cooling and heating, outperforming standard coolers by 80% in cooling power under counter-radiation conditions [5]. To ensure materials work as claimed in real-world settings, an open-hardware platform called FRESCO-board allows low-cost, simultaneous testing of multiple PRC materials, measuring temperature drop and cooling power with sensors for ambient conditions and sky temperature [6]. Accurate measurement is critical: a metrological setup using SI-traceable sensors achieved relative uncertainties below 10% for cooling power, ensuring that claims are reliable [4].
Where do the studies agree, and where do they conflict?
All studies agree that PRC can achieve significant sub-ambient cooling (3.5–5°C) under direct sunlight, with solar reflectances above 90% and atmospheric-window emissivities above 93% [1][2][3][7]. They also converge on the need for standardized testing: [4] and [6] both highlight that current performance reports are often unreliable and propose metrological or open-hardware solutions. However, there is a conflict in reported cooling power: values range from 26 W/m² for a MOF-treated fabric [3] to 78.7 W/m² for a composite film [2], likely due to differences in material design, measurement conditions, and the presence of non-radiative heat transfer. This discrepancy underscores the importance of standardized testing, as [4] and [6] advocate. Additionally, [5] shows that conventional PRC underperforms in cloudy or humid conditions, while [1] demonstrates that microporous glass still works well at 80% humidity, suggesting that material choice matters for specific climates.
About These Sources
This answer is built on 7 peer-reviewed studies — published from 2021 to 2026, 4 from 2024 or later, 7 in Q1 journals, collectively cited 1,475 times — selected as the most relevant from 8 studies that passed quality screening, drawn from 47 papers retrieved from a database of over 500 million.
Sources used in this answer
A solution-processed radiative cooling glass
Developed a microporous glass coating that achieved ~3.5°C cooling during midday and ~4°C at night under high humidity (up to 80%), with high solar reflectance and durability against water, UV, soiling, and high temperatures.
The best of both worlds—a flexible composite film with hierarchical porous structure for sustainable energy harvesting and passive radiative cooling
Fabricated a flexible FPEEK/PVDF-HFP/SiO2 composite film with 97.36% solar reflectance and 93.04% atmospheric-window emissivity, achieving theoretical net cooling powers of 78.7 W/m² daytime and 119.0 W/m² nighttime, plus energy harvesting capability.
Metal‐Organic Frameworks as a Thermal Emitter for High‐Performance Passive Radiative Cooling
Tested five metal-organic frameworks (MOFs) for radiative cooling; UiO-66(Zr) showed 91% solar reflectance and 96.8% mid-infrared emissivity, cooling a fabric by up to 5°C with a cooling power of 26 W/m² at 300 K.
Metrological setup for accurate determination of passive radiative cooling power
Designed a fluid-based calorimetric apparatus with SI-traceable sensors and a thermopile achieving 12.4 mK uncertainty, enabling relative uncertainties below 10% for PRC cooling power measurement across relevant power densities.
A Dual‐Mode Infrared Asymmetric Photonic Structure for All‐Season Passive Radiative Cooling and Heating
Developed a dual-mode asymmetric photonic mirror that achieved 20% infrared asymmetry, providing 80% higher cooling power than a standalone radiative cooler under counter-radiation conditions, and 8°C lower temperature under cloudy skies.
Open-hardware platform for synchronous performance testing of multiple passive radiative cooling materials
Reported FRESCO-board, a low-cost open-hardware platform for synchronous testing of multiple PRC materials, measuring temperature drop, net cooling power, ambient conditions, and sky temperature with real-time data streaming.
Hierarchical-morphology metafabric for scalable passive daytime radiative cooling
Created a hierarchical-morphology metafabric with 94.5% emissivity and 92.4% solar reflectivity via scalable textile manufacturing, cooling a human body ~4.8°C lower than commercial cotton fabric, with mechanical strength, waterproofness, and breathability.