What evidence would prove passive radiative cooling is commercially viable?

Can passive radiative cooling be made cheaply and at scale?

Yes. Several studies demonstrate that passive radiative cooling materials can be manufactured using existing industrial processes and low-cost, abundant raw materials. For example, a hierarchical-morphology metafabric was produced through scalable industrial textile manufacturing routes, achieving high solar reflectivity (92.4%) and thermal emissivity (94.5%) while maintaining mechanical strength, waterproofness, and breathability for commercial clothing [2]. This shows that radiative cooling can be integrated into products people already buy.

Even more strikingly, researchers turned discarded oyster shells into a passive radiative cooling film using calcium carbonate extracted from waste and polyurethane as a binder [3]. The resulting film absorbed only 22% of sunlight and had 95% emissivity in the atmospheric window, cooling up to 7°C below ambient under 650 W/m² solar irradiance. This approach not only reduces material cost but also contributes to carbon sequestration and waste reduction, directly addressing sustainability and cost concerns.

Other low-cost routes include a 3D porous polydimethylsiloxane (PDMS) film made using citric acid templates, which achieved 78.6% solar reflectance and 99.4% thermal emissivity, and was described as compatible with mass production [5]. Similarly, a thin paint using hexagonal boron nitride plates achieved 96.3% solar reflectance and 92.7% thermal emissivity at a thickness of only 150 micrometers, reducing material usage and cost [13]. A nanoparticle mixture coating using Al₂O₃, SiO₂, and Si₃N₄ nanoparticles was fabricated via a simple one-step spin-coating process, achieving 4% solar absorption and 88.7% selective emissivity [10]. A review specifically notes that nanoparticle-based coatings are preferred for commercialization due to low cost, large-scale production capability, and simplicity [11].

Do these materials survive real outdoor conditions and actually cool?

Yes, multiple studies show that passive radiative cooling materials maintain performance under real-world conditions, including UV exposure, heat, dust, and moisture. A critical review on anti-environmental aging identifies failure mechanisms and design strategies to ensure long-term durability, such as UV resistance, thermal stability, and self-cleaning surfaces [6]. This directly addresses a key barrier to commercialization.

In outdoor tests, a hierarchically structured ceramic achieved 99.6% solar reflectivity and provided continuous subambient cooling with a cooling power over 130 W/m² at noon, while also demonstrating weather resistance, mechanical robustness, and the ability to depress the Leidenfrost effect [1]. A silica aerogel with 98.1% solar reflectance and 92.1% atmospheric window emittance passed environmental aging and thermal vacuum outgassing tests, and a box covered with it achieved an average subambient cooling of 18.6°C under sunlight [4]. This aerogel also resisted temperatures up to 830°C, making it suitable for buildings and spacecraft.

A thin paint with a porous structure and a contact angle of 154° (superhydrophobic) showed excellent durability under dust contamination, and outdoor experiments demonstrated a 2.3°C lower subambient temperature compared to a reference coating [13]. When sprayed on a 3D heat sink, it achieved a 15.7°C lower temperature than a reference 1D structure, proving its effectiveness for heat dissipation. In a tropical savanna climate, radiative cooling paints reduced roof temperature by 12.36°C at midday and saved 335 W/m² of energy on air conditioning [7]. An ultrathin microsphere-polymer film achieved a 7.1°C temperature drop in a rooftop test and was described as mass-producible and economically viable [8].

Even in high-power electronics, a polyethylene film replaced a glass window in a laser package, reducing window temperature by 9.4°C, lowering threshold current by 54 mA, and increasing output power by ~50 mW [9]. This demonstrates that radiative cooling works in thermally constrained commercial devices.

What are the limits? When does it not work well?

Passive radiative cooling is not a universal solution; its performance depends on weather conditions and design trade-offs. A direct comparison between radiative cooling and evaporative cooling under a clear night sky found that evaporative cooling performed better in hot, dry conditions (subambient temperatures of -15.0°C vs. -13.5°C at 13% relative humidity), while radiative cooling was more resilient under high humidity or low temperature (subambient temperatures of -11.5°C vs. -10.5°C at 32% relative humidity) [12]. This means radiative cooling is less effective in humid climates, though it still provides significant cooling.

Another trade-off is between thickness and performance. High solar reflectance is often achieved by increasing coating thickness, which raises material cost and impairs heat transfer [13]. However, the thin paint study solved this by using high-backscattering particles, achieving 96.3% reflectance at only 150 μm thickness [13]. Similarly, the microsphere-polymer film achieved high performance at ~8 μm thickness [8], showing that thin designs are possible.

Some designs sacrifice spectral selectivity for simplicity. A nanoparticle mixture coating achieved selective emission (88.7% within the atmospheric window) and low solar absorption (4%), but its subambient cooling was modest (2.8°C for surface cooling) [10]. In contrast, broadband emitters like the ceramic achieved higher cooling power but may be less efficient in humid conditions [1]. The choice depends on the application and local climate.

Finally, environmental aging can degrade performance if not addressed. UV exposure, thermal cycling, and surface contamination can reduce solar reflectance over time [6]. However, the studies here show that proper material selection (e.g., ceramics, superhydrophobic coatings, aerogels) can mitigate these issues, enabling long-term commercial use.

About These Sources

This answer is built on 13 peer-reviewed studies — published from 2021 to 2026, 6 from 2024 or later, 6 in Q1 journals, collectively cited 1,852 times — selected as the most relevant from 15 studies that passed quality screening, drawn from 47 papers retrieved from a database of over 500 million.

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