A new type of transparent film could help keep cars much cooler in hot weather—without using any electricity.
Researchers from Seoul National University, working with Massachusetts Institute of Technology, Hyundai Motor Company, and Kia, have developed a special coating for car windows that can lower the temperature inside a vehicle by up to 6.1°C.
Anyone who has entered a parked car on a hot summer day knows how quickly the inside can heat up.
Sunlight passes through the windows and gets trapped, causing the cabin temperature to rise sharply.
This not only makes the car uncomfortable but also increases the need for air conditioning, which uses extra energy and fuel.
Traditional window coatings, such as tinted films or Low-E coatings, can block some sunlight, but they do not remove the heat that has already built up inside.
The new technology works differently. It uses a concept called radiative cooling, which allows heat to escape from the car and be released into the atmosphere.
The research team created a large-area transparent film with a special layered structure. This film lets more than 70 percent of visible light pass through, so it does not block the driver’s view.
At the same time, it reflects much of the sun’s near-infrared heat and sends heat from inside the car back out in the form of mid-infrared radiation. In simple terms, it both blocks heat from coming in and helps push heat out.
To test how well it works, the researchers carried out real-world experiments using actual vehicles.
These tests were done in different countries, including Korea, the United States, and Pakistan, and under a variety of conditions such as summer and winter, parked and moving cars. In all cases, cars fitted with the film stayed cooler than those without it.
The results showed not only a lower cabin temperature but also reduced energy use.
Cars with the film needed less air conditioning, cutting cooling energy consumption by more than 20 percent.
The film also helped the car reach a comfortable temperature faster, reducing the waiting time by about 17 minutes after turning on the air conditioner.
Although the film slightly increases the need for heating in winter, the energy savings in summer are much greater overall. The researchers estimate that if this technology were used in all passenger vehicles in the United States, it could reduce carbon dioxide emissions by about 25 million tons each year. This is roughly equal to taking around 5 million cars off the road.
The study, published in Energy & Environmental Science, shows that this transparent cooling film is not just a laboratory idea but a practical solution that works in real driving conditions.
It offers a simple way to make cars more comfortable, save energy, and reduce environmental impact—all without using extra power.
