New Whitest Paint Might Help Fight Climate Change

It’s hot! Hotter than it used to be, and too hot for things to remain nice in the future. The sun keeps beating down, and as our greenhouse gas emissions continue to blanket the earth, more of that heat is trapped, leading to the steady uptick in global average temperatures. Reducing these emissions can help, but there’s other possibilities too. A team of researchers with a new very white paint think it might be of some use in solving the problem.

Thermal imaging shows the white paint’s ability to cool a surface below ambient temperature, by radiating away excess heat.

The new “whitest white” paint comes to us from Purdue University in the US. It’s capable of reflecting 98% of sunlight reaching its surface, a big step up over the typical 80-90% of conventional white paints. Additionally, it doesn’t absorb UV light, and can also radiate out heat in infrared wavelengths that pass out of the atmosphere. This allows the paint to cool surfaces below ambient temperature. The paint achieves these feats by using barium sulphate as a pigment, which doesn’t absorb UV like conventional titanium dioxide white pigments do. The paint also uses a lot of pigment – 60%, versus 20-40% in a more typical paint. This is similar to techniques used in producing Vantablack, the blackest black acrylic paints.

The hope is that by painting roofs and walls of buildings with white paint, more sunlight will be reflected back out into space, and buildings will be naturally cooler with less reliance on air conditioning, helping to reduce emissions. This could go a long way to solving the heat island effect in many major cities. Municipalities around the world have already begun adopting the technique, from California, to New York and Ahmedabad. It’s an easy thing to do, with few drawbacks, so we expect to see the practice grow more popular in coming years. While it won’t solve the climate crisis on its own, the world could surely use every bit of help it can get.

66 thoughts on “New Whitest Paint Might Help Fight Climate Change

  1. I had worked here we had an ice freezer; the white steel remained relatively cool in the sun, however that
    ‘hammered aluminum door’ easily burned my hand. Probably designed by the power company.

      1. And how do you plan to store this heat until the next cool period comes along?

        this comment is like saying “I wont drink so I don’t have to flush later, I’m saving water twice!”

  2. This is good, but roves do get dirty, especially if birds are involved. So unless this is mixed in with some sunflower seeds and fed to the respective birds, it’ll degrade with time.

    Not wishing to be too much of a naysayer. The muck issue was reported last time I read something about extra white paint. Can’t find link.

    It is a good solution as any degree of additional white has to be a good thing for reflecting heat.

    1. Bill Clinton has been espousing white roofs for quite a while now, and while you can argue the exact efficacy of such a change it’s impractical to suggest that white roofs would not lower your energy costs. It just doesn’t happen because society does not find it fashionable, and that’s the first problem you have to overcome before you delve into how to keep the roof clean.

        1. that article is an opinion piece about low-slope commercial roofs – with no numbers or facts ie it is meaningless.

          If you look at something with actual numbers for a roof product – ie colorbond steel – http://steel.com.au/products/coated-steel/colorbond-steel/basix-and-bca-classification you will notice a huge difference between different colors.

          Indeed, I changed the rood of my holiday house (in the tropics) from a color darker than ‘deep ocean’ (solar absorptance at least 0.75) to that of surfmist (.32). The difference in summer – with the same insulation in the roof – was huge.

          I do agree that it’s got a reasonable slope, and that there is quite a bit of rain in the wet season to give it a clean.. But virtually no amount of dirt could make it as bad as a dark roof!

  3. And here in Europe we call it RAL9016, or well, that the color code I use on the walls inside.
    Point is we should use it everywhere outside. It will be a bright world.
    Do it.

  4. On earth day wondering what spreading barium sulfate allover roofs and walls will do to the world. Knowing it started right across the Wabash river makes it come home. We have a intentionally mispronounced phrase here in town “you’re-duna perversity”. Could this be? Will they paint all that requisite red brick white?

  5. doesn’t radiate away excess heat better because it is white. In fact the opposite is true. It radiates less effectively in the far infra red. What it does do is reflect incident radiation better. That is the cooling effect.

    1. You got it exactly wrong. Though it does absorb less visible spectrum than most other white pigments, the real win is that it is *dark* in the far infrared, and so is an effective radiator at those thermal wavelengths.

      If all you want is high reflectivity, use Teflon: it’s even better than this stuff. Easy to clean too! But it’s also white at 10um thermal wavelengths, so makes a lousy radiator.

  6. Hidden in the effusive ignorance of that Guardian article (can’t fault them too much — they’re just parroting the dumbed-down-for-public release from Purdue’s PR droids) is the key point: It’s NOT that this stuff reflects more than big-box-store paint — it’s only really absorbing 10% less power, after all.

    The key point here is that barium sulfate is highly absorbing (and thus, by reciprocity, highly *emissive*) around 10 microns wavelength — the peak of radiation from objects around 40 C. Most of the other current pigments for white paint remain reflective around there.

    So this stuff radiates away a few hundred watts per square meter at thermal wavelengths, while absorbing somewhat less from the sun *at the same time*. It’s a neat trick. More information is available in any number of textbooks, including the 1978 Infrared Handbook that’s on my 3-foot bookshelf (You know: 3 feet of your most important books, three feet from your desk… from Dr. Eliot) .

    It’s an even neater trick to turn this into something newsworthy, since it’s been known for decades. But I guess even Purdue’s technology licensing office is just as hungry as the rest of them.

    1. Disbelievers will immediately jump in and say “That’s impossible! The sun is much hotter than the sky! There’s no way you can radiate more thermal power from a surface than you receive in sunlight!”

      But it’s true, because the sun is tiny: You’re receiving power from a hot object that is just 7e-5 steradians in size, but radiating away to a cold sky that’s effectively 4-5 steradians big: >50 thousand times larger.

    2. Yeah, k, great, that is fine. But isn’t global warming caused my IR being trapped in the atmosphere due to excess CO2? Why would radiating more out into the atmosphere be a good thing?

    1. Not unless you’re talking about a front-surface mirror with fancy and fragile dielectric coatings.

      A plain mirror absorbs ten times more light (10%) than a good white coating (1%).

  7. The surface area of the tops of all human dwellings is too small an area to affect earth’s temperature below it. A better idea would be to let the earth’s own hydrologic cycle regulate it’s own temperature. Yes this comment is trolling. Yes, I am correct.

    1. Yes, correct, but incomplete: Reducing heat absorption and promoting thermal radiation help a bit, but a bigger win is the reduced energy input required to cool the space below, and the associated multiplier effect on reduced thermal output from the power plants producing that energy.

      But depending on the local environment it’s arguable you’ll get a bigger win by just putting in a bit more insulation, and thereby also reduce the energy input required to *heat* the space at night or in winter.

  8. If one paints the walls that color then I would imagine that dead patches of lawn would be soon to follow. The summer sun facing windows on my house would kill big fuzzy edged rectangular patches of grass every late spring to early fall because of the nice southern sun rays reflecting off my energy star windows and white backed blackout curtains.

    1. It depends on how you define “ambient temperature”. If you say it’s the local air temperature, then it’s certainly easy to get less than that by thermally radiating power away to someplace colder, like space. At room temperature, you’re radiating hundreds of watts per square meter away all the time. You don’t lose heat, though, because (usually) your environment is radiating about that much right back at you. But if you have a clear view of the cold universe above, you’ll lose heat quickly, and it’s easy to get below local air temperature.

      It’s old news. Heck, Egyptians made ice this way a thousand years ago.

      1. – Wow – wrapping my head around this still… So it’s more about reference to absolute zero (?) than ambient – if above, you’re radiating heat to some degree – and under generalized ‘usual circumstances’ objects can absorb heat from ambient air / surroundings at a high enough rate to make up for this. So is it really a clear night allows the object to directly radiate out, or moreso a clear night is letting ‘everything’ radiate out with less reflection? – I.E. a bucket of water at night – normally may be absorbing energy radiated from surrounding lands/buildings/etc being reflected back by cloud cover – but a clear night – radiations of the water (and surroundings) do not reflect back. My gut is it is the reflections of radiations from ‘everything else’ on a cloudy night which keep the bucket from loosing heat at a fast enough rate to drop below ambient temps, rather than it’s own particular reflections… Minor nit pick, but I feel it’s moreso ‘the local system’s clear view of the sky’ than the bucket/pool of water itself at play here to let water drop below ambient (in egyptian ice case specifically) with clear sky view at night. Might have to do some research here – quite interesting…

    1. Oh dear. That doesn’t sound like much.That’s only 6 times more than we have copper on the planet. And only 30 times more than we have lead.

      We better not squander it by spreading it thousands of atoms thick on roof coverings.

          1. I’m sorry. I don’t see what is troubling you so much about this.
            No maths, no lies, no games at play here. I’m Just reporting what just about any person connected to the internet can easily look up themselves. For example, Google’s first hit on the subject: https://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth%27s_crust

            If you need an explanation on how “to actually do the maths” to divide one number by another to get the ratios I quote, then I suggest you find someone local to help you with that.

    1. “What about in winter? Increased heating costs?”

      What’s winter? I live in Florida… Winter doesn’t matter, it’s the global warming, and well, the pandemic, that the only thing you need to think about. Computer models predict, we’ll all be burned to a crisp in 30 years…

  9. You sound like 70% of the spam I receive (I don’t filter spam: I sometimes look into it, out of a weird curiosity for psychological deviances. Some day, I’m gotta make a statistics, with R and colorful pics and that).

  10. I would really like it to be available for purchase at hobby stores or suppliers, but with ROHS nonsense and thorough lead bans, do you expect “barium sulphate” containing paint to be released to public use?

    1. It’s not just about total “percentage of the Earth’s surface.” As mentioned above, urban heat island is a real problem. In the suburbs, this could make a big difference

  11. Now can they make it so it changes to Vanta Black when I need to warm my house? I live with cold winters and warm summers. And I definitely spend more money heating. I need a roof and walls that can change colour according to the temperature or the season.

  12. Barium Sulphate? Really? Its also called Blanc Fix and is quite an old pigment.
    Back in the days when paint was sold comercially by weight and not by volume it was used instead of Titanium Dioxide because it is really heavy and so the paint was made more “valueable” ;-)
    So, what I am saying is … it is an old pigment, maybe even ancient.
    So the article fails a little in this regard since it sells it as a novelty. I haven´t read the referred article yet, but I am assuming that the real novelty is a new process of refining the barium sulphate in order to maximize its reflectivity over a huge wavelength range in order to make it “whiter”.

    1. I found this trying to figure out how cheap I could make an integrating sphere a few years ago. Barium Sulphate in house paint is a very old idea.
      https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1010&context=cpl_techniquesinstruments

      This is probably the more interesting part for the paint portion since its about the particle size. New article is mostly about temperature testing.
      https://engineering.purdue.edu/NANOENERGY/publications/Peoples_IJHMT_2019.pdf

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