As electricity demand for air conditioning rises and extreme heat puts growing pressure on homes, offices and power systems, researchers are advancing a cooling technology that works without a compressor, refrigerant or continuous electricity input. Known as passive daytime radiative cooling, the approach uses specially engineered surfaces to reflect most incoming sunlight while releasing heat as infrared radiation through a relatively transparent part of Earth’s atmosphere and towards the cold of outer space.

Recent research is moving the technology beyond laboratory demonstrations and towards coatings, films, roof materials, textiles and hybrid systems. A 2026 review in ACS Applied Materials & Interfaces describes rapid progress in radiative-cooling structures and their commercial applications, while a July 2026 review in RSC Advances examines how materials are being designed to survive real-world conditions such as humidity, dust, ultraviolet exposure and extreme weather.

Scientific diagram explaining passive radiative cooling and the exchange of heat between a roof, the atmosphere and outer space
How radiative cooling works. Reproduced from Zhu et al., Light: Science & Applications (2022), under CC BY 4.0.

How can a surface cool itself under the sun?

Most familiar cooling systems remove heat using electricity. An air conditioner, for example, transfers heat from indoors to outdoors through a refrigeration cycle. Radiative cooling takes advantage of a natural physical process: all objects emit thermal radiation, and the atmosphere has a wavelength range — commonly described as the 8-to-13-micrometre atmospheric window — through which some infrared energy can escape more readily into space.

To make this process useful during the day, a radiative-cooling material must perform two jobs at once. It needs to reflect a very large share of sunlight so that it does not become hot in the first place, and it must emit thermal energy effectively in the infrared range that can pass through the atmospheric window. If the balance is right, the surface can lose more heat than it gains and may become cooler than the surrounding air, even in sunshine.

This is not the same as creating cold from nothing. The material is managing the flow of energy between the surface, the atmosphere and space. Its performance depends on the material’s optical properties as well as cloud cover, humidity, wind, the angle of the sky visible to the surface and how the material is installed.

From advanced films to reflective cooling paints

Researchers are investigating several material families. Photonic and metamaterial structures use carefully designed layers or microscopic patterns to control how different wavelengths of light and heat interact with a surface. Porous polymers and particle-filled coatings scatter sunlight, helping prevent solar energy from being absorbed. Other approaches use ceramic particles, silica, calcium carbonate, barium sulphate and engineered polymer structures to achieve high solar reflectance and strong infrared emission.

One important direction is to make radiative cooling easier to manufacture and apply. A sophisticated multilayer material may perform impressively in a laboratory but be too expensive or difficult to produce over thousands of square metres. Paint-like coatings, sprayable films and roll-to-roll manufactured materials could be easier to scale because they can potentially be applied to existing roofs, walls and equipment using familiar industrial processes.

A 2026 review of materials for extreme-weather applications summarizes reported benchmark systems with solar reflectance around 0.95–0.98 and infrared emittance around 0.90–0.96. Under favourable clear-sky test conditions, some systems recorded daytime surface temperatures roughly 4.5–4.9°C below ambient air. These are research benchmarks, not guaranteed results for every building or climate.

What outdoor experiments have demonstrated

In a 2022 open-access study published in Light: Science & Applications, researchers investigated a dual-sided thermal-management design intended to reduce heat entering buildings and other temperature-controlled enclosures. The system combined a specially engineered outer film with an inner radiant barrier, allowing the roof to reject heat while limiting the amount transferred into the room.

Outdoor experimental setup used by researchers to test radiative cooling films on model roof enclosures
Outdoor experimental setup comparing roof treatments. Reproduced from Zhu et al., Light: Science & Applications (2022), CC BY 4.0.

The researchers reported that, in their controlled outdoor experiments, the system lowered the average indoor temperature of test enclosures by between 2.3°C and 5.8°C compared with untreated roof controls, depending on roof colour. In a separate test where the enclosures were maintained at about 26°C, the design reduced the measured cooling load by up to 63% compared with the bare-roof control.

The result is significant because it demonstrates a possible role for radiative cooling beyond making an exposed panel colder. A roof treatment that reduces the heat entering a room could help an existing air conditioner work less, potentially lowering electricity consumption. However, the study used a controlled test setup; the reported saving should not be treated as a universal reduction for every house, office or air-conditioning system.

Research charts and measurements showing heat flux and cooling energy performance of radiative cooling roof treatments
Experimental energy and heat-flux measurements. Reproduced from Zhu et al., Light: Science & Applications (2022), CC BY 4.0.

Why the technology could matter for buildings and cities

Roofs and exterior walls receive substantial solar energy. In hot regions, that heat can raise indoor temperatures and increase the workload of air conditioners. A durable radiative-cooling roof coating could reduce heat absorption before it enters a building. At scale, lower cooling demand could help reduce electricity bills, ease peak demand on electricity networks and cut emissions where power generation relies on fossil fuels.

The potential applications extend beyond houses. Researchers are exploring radiative cooling for warehouses, factories, data-centre equipment, vehicles, solar panels, greenhouses, agricultural storage and outdoor infrastructure. Some materials are being designed to preserve visible colours or allow light through, opening possibilities for windows, façades and surfaces where a conventional opaque white coating would not be suitable.

Textile research is another emerging area. A 2026 review in Materials Today Physics describes progress in fibres and fabrics designed to reflect sunlight and release body heat. Such materials could eventually contribute to personal thermal comfort for people working outdoors, although breathable performance, durability, washing and real-world cooling benefits still require careful testing.

The tropical climate challenge: humidity and clouds

One of the most important limitations is atmospheric moisture. Water vapour absorbs infrared radiation, reducing the amount of heat that can escape through the atmospheric window. Clouds can also obstruct the radiative pathway. This means a material that performs exceptionally well in a dry, clear-sky laboratory test may deliver a smaller cooling effect in a humid, cloudy environment.

This issue is particularly relevant to tropical coastal cities and regions such as southern Nigeria, where high humidity, cloud cover and seasonal rainfall are common. In these conditions, radiative cooling may still help by reflecting sunlight and reducing the amount of heat absorbed by roofs, but achieving a surface temperature below ambient air is less reliable. The practical objective may therefore be reducing heat gain and air-conditioning demand rather than promising dramatic sub-ambient cooling throughout the day.

The 2026 review in RSC Advances identifies humidity, dust accumulation, ultraviolet ageing, moisture penetration and seasonal overcooling as major barriers to long-term outdoor use. It emphasizes that performance must be assessed under realistic weather conditions rather than inferred solely from short laboratory demonstrations.

Durability, cost and maintenance remain decisive

For a cooling coating to become commercially useful, it must retain its reflectivity and infrared properties after years of exposure to sunlight, rain, dirt, pollution and physical wear. Dust and grime can darken a highly reflective surface, reducing the sunlight it sends away. Moisture can damage some porous or polymer-based structures, while ultraviolet exposure can gradually degrade certain materials.

There is also a trade-off between performance and affordability. Highly engineered multilayer structures may offer precise optical control but require specialised manufacturing. Simpler paints may be easier to scale, but their performance can vary with coating thickness, surface preparation, formulation and weathering. Researchers are therefore looking for materials that combine high reflectance, strong infrared emission, low toxicity, easy application and long service life.

Could radiative cooling replace air conditioning?

At present, it is more realistic to view radiative cooling as a potential complement to conventional cooling rather than a universal replacement. It does not provide the same controllable cooling capacity as an air conditioner, and its output changes with the weather and the amount of sky visible to the surface. Buildings also need insulation, ventilation, shading and sensible design to manage heat effectively.

Hybrid systems may offer a more practical route. Radiative cooling can be combined with evaporative cooling, ventilation, thermal insulation or water-harvesting materials. The aim is to build systems that continue to provide useful cooling when humidity, cloud cover or other environmental conditions reduce the performance of any single method.

What comes next?

The next phase of development will depend on independent outdoor testing, larger demonstration projects and evidence of energy savings over full seasons. Researchers will need to compare materials across different climates, measure how quickly coatings become dirty or degrade, and establish realistic installation and maintenance costs. Building owners and policymakers will also need reliable standards so that performance claims can be compared fairly.

Passive radiative cooling is not a magic solution to rising temperatures or electricity demand. But it offers a scientifically grounded way to manage heat using the natural exchange of infrared energy with the sky. If researchers can make the materials durable, affordable and effective in humid as well as dry climates, the technology could become a useful part of the wider effort to make buildings, infrastructure and cities more resilient to heat.

Research and reference sources