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The whitest paint ever created by humans reflects 98.1% of all solar light it receives and makes the surface cooler than the air around it even under strong sun at noon
All white paint reflects sunlight. Everyone knows that. But the paint that a team from Purdue University in the United States created in 2021 does something that no commercial paint can.
It reflects 98.1% of all solar radiation that hits the surface. Common white paints reflect between 80% and 90%. The difference seems small, but it changes everything.
Because when a paint reflects more than 95.5% of light, the surface not only stops heating up.
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It cools down. It becomes cooler than the air around it.
In outdoor tests, Purdue’s paint managed to cool the surface by up to 4.5 degrees Celsius below the ambient temperature. Without electricity. Without a mechanism, just paint.
The achievement entered the Guinness World Records as the whitest paint ever recorded.
The secret is in barium sulfate and the size of the particles
The team led by professor Xiulin Ruan tested over 100 combinations of materials before arriving at the final formula.
The key ingredient is barium sulfate, a white mineral compound used in photographic papers and in medical contrast exams.
But it’s not enough to just use any barium sulfate.
The trick is in the size of the particles. The researchers used particles of varying sizes, each reflecting a different wavelength of solar light.
Together, they cover almost the entire solar spectrum, from visible light to infrared.
It’s like having a team of players where each covers a different position on the field, no light gets through.
Radiative cooling: the principle that makes the magic work
What the paint does has a scientific name: passive radiative cooling.
In simple terms, the painted surface emits heat in the form of infrared radiation into space.
Outer space has a temperature close to -270 degrees, it is an infinite sink of heat.
The paint acts like an antenna that transmits heat from the surface directly to the universe.
The more sunlight it receives, the more heat it returns. And the final balance is negative: the surface cools down.
Common white paints cannot achieve this effect because they absorb 10 to 20% of the radiation. Purdue’s paint absorbs less than 2%.
The impact on the electricity bill: a 93 square meter roof saves 10 kilowatts
The researchers calculated that painting the roof of a 93 square meter house with this paint is equivalent to a cooling power of 10 kilowatts.
For comparison, most residential air conditioning systems operate between 3 and 5 kilowatts.
In other words, the paint cools more than two air conditioning units running at the same time and without consuming a single watt of electricity.
In hot regions, where the energy bill for cooling can exceed 40% of total consumption, the impact would be enormous.
Entire cities could reduce their energy demand just by changing the color of their roofs.
White Roof Cities: The Concept is Not New, But the Technology Is
In Greece, whitewashed houses have existed for centuries.
In Santorini, the white walls are not just aesthetic; they are functional: they reflect the sun and keep the environments cool.
However, traditional whitewashing reflects only 70 to 80% of the light.
Purdue’s paint does what the Greeks have always wanted, but with 98.1% efficiency.
Urban planning projects are already discussing painting roofs and sidewalks white in cities like Los Angeles, New Delhi, and São Paulo to combat heat islands.
With ultra-white paint, these projects could have much more significant results.
Is the Paint Already on the Market?
In 2022, Ruan’s team partnered with a company to produce the paint on a commercial scale.
The first versions are already available in limited quantities.
The cost is still higher than conventional paints, but it is expected to decrease with the scale of production.
Barium sulfate is abundant and cheap. The challenge is to maintain the particle size distribution in industrial production.
The expectation is that in a few years the paint will be available in regular hardware stores.
What It Does Not Solve
The paint does not work well on surfaces that do not receive direct sunlight.
Walls in the shade or facades facing south in the southern hemisphere do not benefit as much.
On cloudy days, the cooling effect decreases significantly, and the paint only works on external surfaces. Painting an internal wall with it will not cool the room.
Moreover, maintaining pure white requires cleaning. Dust and dirt reduce reflectivity.
Even with these limitations, the cost-benefit ratio is unmatched.
No active cooling technology can work for free, forever, with zero electrical maintenance. The whitest paint in the world can.
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