What are the main safety and reliability risks of passive radiative cooling?
The biggest safety risk identified across these studies is fire. Many PRC materials are polymer-based, which are inherently flammable. One paper [3] explicitly states that 'radiative cooling materials represented by polymers have a high fire hazard.' Another [5] notes that the practical application of PRC coatings is 'often limited by the lack of reliable binders' and that traditional organic polymer binders still pose fire threats. This is not a hypothetical risk—it's a known limitation that has held back real-world adoption.
A second major risk is 'overcooling'—the material keeps radiating heat even when you don't want it to, like on a cold winter night or in a cool climate. One study [2] calls this out directly, saying current PRC materials 'suffer from a range of issues, including overcooling during night/winter.' This can make a building uncomfortably cold or increase heating costs, undermining the energy-saving purpose.
There are also reliability concerns tied to durability and manufacturing complexity. For instance, early PRC designs used nanophotonic multilayers or 2D/3D pillar arrays that are 'complex and costly to manufacture,' limiting large-scale use [1]. Another study [5] highlights that many PRC coatings lack durable binders, which means they may degrade or fail over time under real weather conditions.
How are researchers making PRC safer and more reliable?
Researchers are tackling the fire risk head-on by embedding flame retardants directly into the cooling material. One team [2] created a wood-derived aerogel that integrates magnesium-aluminum layered double hydroxide nanoflakes, which serve as both thermal emitters and flame retardants. The result: the aerogel has 'superior fire safety, with a low heat release rate and negligible smoke production' while still achieving 15.6°C of sub-ambient cooling in summer. Another group [3] used diatomite-based melamine-phytates in a PVA aerogel, which forms a protective char layer and releases non-combustible gases when heated, giving 'superior fire resistance.' Both studies show that fire safety and high cooling performance are not mutually exclusive.
To solve the overcooling problem, the same wood-derived aerogel [2] was designed for 'all-season thermal management.' It provides a 'considerable net warming effect of 2.1°C on winter nights' thanks to its ultralow thermal conductivity (0.043 W/m·K), which traps heat when the sky is cold. This is a clever design: the material switches from cooling mode in summer to insulating mode in winter, without any moving parts or energy input.
For reliability and scalability, simpler and cheaper manufacturing methods are being developed. Instead of complex nanophotonic structures, researchers are using nanoparticle dispersions (e.g., TiO₂, SiO₂, Al₂O₃) that are 'simpler and cheaper to make and can be scaled more easily' [1]. One study [4] used an electrospun polyvinyl alcohol film with embedded SiO₂ and Al₂O₃ nanoparticles, achieving a solar reflectance of 0.88 and thermal emissivity of 0.95—good enough to keep a smartphone battery 22.9°C cooler under direct sunlight. This shows that practical, durable PRC is possible with off-the-shelf materials.
How much do these improvements matter in real-world use?
The improvements are substantial. The fire-safe aerogels [2][3] not only pass fire safety tests but also outperform many previous PRC materials in cooling power. The wood-derived aerogel [2] achieved 15.6°C sub-ambient cooling in summer, which is among the best reported. The PVA aerogel [3] reached 15.3°C cooling under extreme solar intensity (738 W/m²) and showed 'significant energy saving under different climatic conditions around the world' in simulations. These are not lab curiosities—they are designed for real buildings and cold-chain logistics.
For reliability, the nanoparticle-based coatings [1] and electrospun films [4] show that PRC can be made durable enough for outdoor use. The radiative cooling film [4] kept wearable sensors at an average of 42.5°C—up to 8.6°C cooler than unprotected sensors—and prevented thermal failure. It also reduced a smartphone battery's peak temperature from 60.0°C to 37.1°C, which is a huge reliability and safety gain for electronics.
However, not every design works perfectly. One study [1] found that a skylight system using nanoparticle coatings on Cleartran glass achieved only modest cooling gains (e.g., sky-directed LW flux increased from 39 to 54 W/m² with air as the gas), and the performance depended heavily on the choice of gas inside the skylight. Some gases (like HFC-125) have very high global warming potential and are now restricted, while others (like ammonia) have safety constraints in residential use. This means that real-world reliability still requires careful material and gas selection—there is no one-size-fits-all solution yet.
About These Sources
This answer is built on 5 studies (4 peer-reviewed, 1 preprint) — published from 2025 to 2026, 5 from 2024 or later, 2 in Q1 journals — selected as the most relevant from 5 studies that passed quality screening, drawn from 41 papers retrieved from a database of over 500 million.
Sources used in this answer
Experimental and Numerical Investigation of a Skylight System for Daytime Passive Radiative Cooling
This dissertation experimentally and numerically tests a passive radiative cooling skylight, finding that nanoparticle coatings and low-GWP gases (HFC-152a, HFC-41) can achieve daytime cooling, but performance depends heavily on gas choice and geometry; some gases (HFC-125) are restricted due to high GWP, and ammonia has safety constraints.
A Flame‐Retardant, Thermal‐Insulating Wood‐Derived Aerogel toward All‐Season Thermal Management
This study develops a flame-retardant, thermal-insulating wood-derived aerogel that achieves 15.6°C sub-ambient cooling in summer and a 2.1°C warming effect on winter nights, with ultralow thermal conductivity (0.043 W/m·K) and superior fire safety (low heat release, negligible smoke).
Fire safety protective polyvinyl alcohol-based “green” aerogels with micro/nano dual-scale porous structure for passive radiative cooling
This paper creates a PVA-based 'green' aerogel with micro/nano dual-scale pores and embedded flame retardants, achieving 15.3°C cooling under 738 W/m² solar intensity, high solar reflectance (91.47%), high infrared emissivity (92.98%), and superior fire resistance via a protective char layer.
Thermal protection of wearable devices under outdoor conditions using radiative cooling films
This study fabricates a radiative cooling film via electrospinning of PVA with SiO₂ and Al₂O₃ nanoparticles, achieving solar reflectance of 0.88 and thermal emissivity of 0.95; it kept wearable sensors up to 8.6°C cooler and reduced a smartphone battery's peak temperature from 60.0°C to 37.1°C under direct sunlight.
A Scalable, Durable, Fire‐Safe All‐Day Passive Radiative Cooling Coating for Sustainable Buildings
This paper (abstract only partially available) discusses a scalable, durable, fire-safe all-day passive radiative cooling coating, noting that practical application is often limited by the lack of reliable binders and that traditional organic polymer binders still pose fire threats.