The Whitest Paint Ever Could Cool Cities and Fight Climate Change

Jun 4

In a small lab at Purdue University, where fluorescent lights hum over cluttered benches and beakers hold quiet ambitions, a team of engineers painted a strip of brilliance onto our climate future.

It wasn’t flashy.

It wasn’t loud.

It was white.

So white, in fact, it might just change the temperature of the world.

This isn’t poetic white. Not clouds-in-springtime or milk-in-moonlight. This is engineered white…the most reflective substance ever put in a paint can. It deflects 98.1% of sunlight. It cools surfaces below ambient temperatures. It may become one of the simplest, cheapest, most powerful tools in our climate arsenal.

And all you have to do is brush it on.

The Reflective Power of White

Let’s start with a lesson from the sun.

Sunlight travels 93 million miles to reach us, and Earth absorbs much of that energy.

Dark roofs, asphalt roads, and tar-coated warehouses drink it in like thirsty stone, holding the heat long after sunset. White surfaces (true white) do something else entirely: they send the light back.

Reflectivity is a defense. It’s how light-colored desert animals survive heat. It’s why you wear white on scorching days. But most white paint? It doesn’t do enough. Commercial white coatings reflect about 80–90% of solar radiation. The rest gets absorbed, warming the material beneath.

Purdue’s paint? It reflects 98.1% of sunlight…and it does something no other paint can. It emits infrared heat through a process called radiative cooling, effectively pushing heat into deep space!

Under direct sun, it can cool surfaces up to 8°F (4.5°C) below ambient air temperatures…without using a single watt of electricity.

That’s not a color.

That’s a climate strategy.

What’s in the Paint? The Science of Barium Sulfate

The secret ingredient is barium sulfate, a compound already found in photo paper, makeup, and medical imaging.

But paint is more than ingredients. It’s particle physics in a can.

What Ruan’s team did differently was alter the particle size distribution of the barium sulfate. Instead of uniform particles, they used a variety of sizes, each scattering a different wavelength of sunlight. This creates near-total reflectance across the full solar spectrum…from UV through visible to near-infrared.

Think of it as a symphony of scattering.

Most paints absorb enough heat that they eventually warm up. But this one doesn’t. Its emissivity (its ability to radiate energy) actually allows it to cool even in direct sunlight.
It’s like painting your roof with a sheet of ice that never melts.

The Urban Heat Island Effect: Cities That Burn

Now imagine this paint on a city.

Urban areas trap heat in what scientists call the urban heat island effect. Skyscrapers, concrete plazas, and dark rooftops soak up radiation all day, turning cities into low-simmer furnaces. This heat raises air conditioning demands, strains electrical grids, and worsens pollution…especially in poor neighborhoods without adequate cooling.

In cities like Phoenix, Delhi, Cairo, and even New York, pavement and buildings can drive temperatures up to 7°F (4°C) hotter than nearby rural areas. That’s not just uncomfortable, it’s actually deadly. During heatwaves, these islands of urban heat become pressure cookers for vulnerable populations.

Now coat those buildings with this paint.

Suddenly, the roof isn’t absorbing heat…it’s rejecting it.
Office buildings stay cooler.
Apartment complexes reduce A/C usage.
Asphalt doesn’t radiate warmth back into the sky.
Air conditioners don’t have to work overtime.

The grid breathes easier.

Multiply that across a city block, a borough, an entire metro area. You’re not just painting buildings anymore.

You’re lowering regional temperature.

Radiative Cooling: A Climate Solution from Space

It sounds futuristic, but it’s rooted in ancient thermodynamics.

Radiative cooling refers to the ability of a surface to emit heat as infrared radiation, allowing it to lose energy to the sky, even under sunlight. It’s how deserts cool rapidly at night. It’s how the human body stays cool through sweat evaporation and radiation.

This paint leverages that same principle…but better.

By emitting mid-infrared radiation into the 8–13 micron wavelength range (what scientists call the “atmospheric window”) the paint can release heat directly into space, bypassing the warming layers of Earth’s atmosphere.

This makes it a passive cooling system.
No power needed.
No moving parts.
No refrigerants or chemicals.
Just paint, doing the work of an air conditioner, while reducing the need for one.

And unlike other geoengineering proposals that require mirrors in orbit or giant sulfur injections into the stratosphere, this one isn’t theoretical.

It exists. In a can. Right now.

From Skyscrapers to Straw Huts: Use Cases Across the Globe

Where could this paint go? The better question is: where couldn’t it?

Urban rooftops: To reduce city heat and lower electric bills.
Warehouses & factories: To protect workers from extreme temperatures without the cost of industrial cooling.
Mobile homes & trailers: Especially in low-income areas where insulation is poor and A/C is a luxury.
Off-grid cabins & shelters: Perfect for sustainable architecture that avoids reliance on power grids.
Tents in refugee camps: Offering cooler shelter in crisis zones.
Desert architecture: Reflecting solar heat in the world’s hottest regions.
Humanitarian aid & disaster relief: Painted shelters in post-hurricane or wildfire zones could offer safer, cooler spaces for recovery.

It’s not just about comfort. It’s about access.

Cooling should be a human right. And this paint might make it one.

How Does This Compare to Other Climate Tech?

We’ve seen a surge in climate innovation: solar panels that track the sun, carbon capture machines, lab-grown meat, algae biofuels, and electric everything.

All are vital.

But few are this immediately applicable.

You don’t need legislation to paint a roof. You don’t need a utility company, a subsidy, or a specialized installer. You need a roller and some time. That’s what makes this such a breakthrough—it democratizes adaptation.

It’s affordable. Scalable. Simple.

Which makes it radical.

The Future of Cooling Isn’t Plugged In

We are facing a paradox: the hotter the world gets, the more we rely on cooling systems that increase emissions. Air conditioning already accounts for 10% of global electricity use.
By 2050, that number could triple.

Cooling is one of the great energy dilemmas of the 21st century.

What if we could cool without energy?

That’s what this paint offers…a bridge out of that paradox. A way to cool buildings, cities, and perhaps even regions without consuming more fossil fuel.

Paint enough surfaces, and you start to imagine a different world. A world where summers don’t kill, where cities don’t bake, where relief doesn’t come with a monthly electric bill.

Barriers to Scale: Not All White Paints Are Equal

Of course, this isn’t a magic fix yet.

There are limitations:

Durability: The current formulation may not withstand harsh conditions (like rain, snow, or abrasion) without degradation.
Cost: Barium sulfate is pricier than traditional paint ingredients.
Application requirements: The paint must be applied correctly and may require re-coating after a few years.

But the researchers are already working on improvements, versions for cars, ships, even spacecraft. There's a road ahead, but it’s painted bright.

The Philosophy of Cooling With Color

Sometimes, climate change feels enormous…out of reach, out of time, out of control. But this paint reminds us that solutions don’t have to be massive or loud.

They can be quiet.

Like a brushstroke.

It’s a color that refuses heat. A formula that whispers no. No to combustion. No to the scorched walls of poverty. No to the silent emergency of another summer.

It’s not a panacea.

But it is a beginning.

And sometimes, beginnings are all we need.