Purdue’s Powerful Paint Could Cancel Climate Change

What if a building could stay cool simply because of its paint job? We’re not talking about putting flames on the sides. Purdue engineers have come up with a formulation of white paint that reflects the heat from sunlight and keeps surfaces cooler than their surroundings. Depending on the location, a building with this paint on the roof may not need air conditioning.

Radiative cooling paint is not a completely new animal, but the formulation developed at Purdue is quite impressive compared to commercially-available paints that only reflect 80-90% of sunlight.

Purdue’s paint reflects 95.5% of sunlight. It can keep surfaces up to 18°F cooler than their surroundings, even in direct sunlight. Where does the heat go? The paint radiates infrared heat, so it escapes the atmosphere and goes into deep space.

How does it do this? With abundantly available calcium carbonate fillers — the chalky stuff that antacids are made of. The paint absorbs next to no UV rays because of the wide band gaps in the atomic structure of calcium carbonate. Take a brief tour of this amazing paint after the break.

We wonder how many rooftops and roadways we’d have to paint with this stuff to have a chance at reversing climate change. It’s not terribly expensive to make, so the problem shifts to widespread education and adoption. What do you think?

76 thoughts on “Purdue’s Powerful Paint Could Cancel Climate Change

    1. “not resonant with existing green house gasses”

      that’s sort of a misnomer, people forget that moisture in the air, humidity, is itself a greenhouse gas. Reflecting IR back into the atmosphere isn’t going to help one bit with that.

      Furthermore, literally painting things white that are traditionally black or other dark colors, has the same effect. We don’t need some specialized super expensive paint, just regular old white paint does the trick pretty well.

      We could put up a study and do the math, but I’ll be honest with ya, i re-roofed my last house from a black tar roof to a tin light color, and INSTANTLY our house stayed cooler and our electric bill cut IN HALF during the summer months. Our heat bill didn’t change during the winter. so the old black roof did literally ZILCH to keep our house warm.

      I also did the exact same thing with a school bus. Yellow roof = hot and bad. Giant tub of industrial white paint, nice n cool by comparison.

      We could accomplish more just by mandating that roofing materials be a lighter color without the expense that this paint will surely command. But good luck getting a municipality to pass any sort of effort to move in that direction.

      btw, if you want to talk about massive heaters, look no further than your local parking lots. birds don’t fly around up there for the view, they use the thermals to gain lift. Planting plenty of trees in the parking lots negates this effect and puts carbon back into the ground, but it’s not cheap to have someone come out and deal with the leaves and debris, even though it’s much better in the long run. trees are literally natural air conditioners. They are the thermal mass that keeps the temperatures from fluctuating wildly on the surface of the blue marble. Other than that, we are creating mini-deserts where the temps fluctuate drastically. Couple that with urban sprawl and you get an outdoor climate that’s uncomfortable to be in MOST of the time. Go out and hang out deep in heavily wooded areas, feels great by comparison.

      I don’t understand why humans look for solutions to problems that already have solutions that are cheaper, easier, and less toxic to the environment.

        1. not expensive in what way? it costs toxic chemicals and emissions to produce. Even if all they had to do was re-tool an existing factory to make (which won’t happen, they’ll expand) it would cost a hell of a lot more in every way just to start manufacturing. It’s already cost them r&d cash wise. After that it’s going to cost our ecosystem. Trees do the exact opposite and contribute to our existing ecosystem. Getting rid of tar shingle roofing in exchange for ‘tin’ roofing would reduce the cost of roofing over the lifetime of a house significantly and stop us from producing and dumping that toxic sludge. Simply using existing factories that already produce white pigmented paints do not require re-tooling or expansion. So my question is why do you have to be a troll and not look at the entire context of the situation, rather than looking myopically at the one bit of data that’s fed to you?

          also ‘specialization’ can mean that it’s patent to the point where only one company can produce the product. this ALWAYS significantly increases cost to the end user/consumer. So, to listen to a research group say “it’s not more expensive” does not mean “it won’t cost the consumer more”. And when it comes to building and maintaining structures, the rule of thumb is the cheapest and easiest, not the highest quality or longest lasting, or any other benefit. For any product to be introduced it has to be cheaper AND more effective AND easier. The only other way is regulation enforcing a specific standard of coating.

          1. You’re comparing short term retooling costs to long term semi permanent benefits. And calling me a troll? On top of that, you completely ignored half of my very short comment – that even if this IS more expensive over a 2 or 5 year period, it also has BENEFITS not realized by common white paint. Then you suggest an “alternative” and consider it superior… by ignoring every downside it has. Get a life.

      1. Chopping down a forest to plant a crappy 4 foot tree growing in a small space is pretty damn stupid.

        But clear cutting continues.

        These non-denominational “Mega-Church” are empty and barren 90 perfect of the time. Its overall stupid what humans do. Not to mention the light pollution from car dealerships.

        1. You can buy pre-grown trees. Not super expensive. And ya, clear cutting is pretty dumb, however the applications I am speaking of is a retro-active action on existing infrastructure such as giant black parking lots. I also think it’s HIGHLY IRONIC for religious people to build these stupid gaudy concrete deserts that create a vacuum devoid of life and intelligent thought, quite the opposite of ‘god’ and what the institutions claim to be.
          And while we are on the subject, the size of the tree will increase over time, it’s the lots of species diversity that is the most damaging to not only the environment, but directly to us. We lose all sorts of great science when we lose a species. ALL of our best medicines come from natural places such as old growth forests. Not to mention inspiration for things exactly like this coating, if not the chemical structures themselves that we didn’t know existed before we found it by licking a frog’s butt. :-p

      2. Why humans don’t is probably as you casually say “mandate”. Royal decrees, commands from on high, etc. rub people the wrong way. Are Mediterranean cities that are mostly white mandated? Or is it the obvious choice?

      3. When I (Mike Massen) wrote “not resonant with existing green house gasses”

        to which user:- ‘make it white’ then wrote:-

        “that’s sort of a misnomer, people forget that moisture in the air, humidity, is itself a greenhouse gas. Reflecting IR back into the atmosphere isn’t going to help one bit with that.”

        My reply is:-
        Its not a misnomer at all, GHG’s include CO2, H2O, N2O, CH4 and other volatile industrial generally un-natural compounds. It is likely many don’t know H2O is a more powerful GHG than CO2, that’s just lack of knowledge not any misnomer, i didnt forget Ive studied this and the effect irrefutable. Fortunately its short-lived at approx 7 days per the weather precipitation cycle but, with fossil fuel combustion its replaced immediately and on the increase too ie. Many don’t know this extra water vapor primarily from combustion causes more rainfall and sporadically too as thermal patterns change globally.

        NB. It is going to help reflecting IR back to space if and only if its not in the bands that the GHGs and others dont absorb and then emit randomly in all directions, 50% on average being back down to Earth thus acting equivalent to a blanket effect as demonstrated from Spectroscopy, Radiative Transfer and quantified by the Beer-Lambert relationship.

        IOW. If it can be arranged that the wavelength of IR sent to space is outside the GHG absorbance bands then the net effect cools when otherwise the GHGs warm and with the effect accelerating, so anything cost effective to return our GHG load to pre-industrial times restores the biodome equilibria we had then for which we adapted to for many millennia previously…

        1. til it reflects off and interacts with something that you didn’t coat in whitewash or this paint….

          a flat roof might be the best case scenario for your ‘miracle paint’ that nobody will be able to afford.

          any surface that doesn’t have an angle of incidence that makes it non-reactive to other structures, the ground, etc. will still have that issue.

          i mean, we are literally talking about trying to direct light. When, to be honest, we could save more carbon being put into the atmosphere by unleashing a massive heard of goats onto the kudzu invaded forests of the north and south carolina mountains. Not to mention the job creation and the amount of people you can feed with the goats.


          or tax the carbon/fuel for cruise ships correctly,

          which would provide every economy they touched with money they should be paying (but don’t currently stateside by registering in foreign countries) AND reduce the size and scope of the abominations they call cruise liners.

          as of right now, with no hard evidence and the fact that a study of such scope may likely never be completed, this white paint is the very low on my list of effective ways to combat climate change and green house gases.

          so take it for what it’s worth, but realistically speaking we need to reverse desertification. Which is what i think is happening in california right now because they killed off all the apex predators, namely the brown bear. It has been shown in many ecosystems to be detrimental to unbalance the ecosystem in such a way. California did so about 100 years, which according to Joh D. Liu and many other ecosystem specialists, is roughly the time scale of which such a thing happens. Don’t even get me started on the relationships between mycelium and fauna in regards to those apex predators and their prey.

          You’ll excuse me if i don’t believe that a white paint is going to solve so many issues, it’s literally like throwing a pebble onto the beach and saying “there’s our break wall”. Just seems a little misguided if you ask me, which nobody did, which is why so many people put so much effort into non-solutions.

          if you want to learn more about how to actually combat climate change, look no further than nature, and look up “reversing desertification”. The best part is, you can literally start in your own back yard. Most people don’t have a compost bin, yet they are the cheapest and most effective way that you can start to offset your own carbon, taking power directly by your own actions. When this paint releases, i might look into it, but i’m not going to hold my breath as it will likely be out of the price range of normal humans, and I can spend my time gardening and rehabilitating old dying trees and be much more effective.

    1. I’ve had suspicions for years about the superiority of whitewash, however, no suitable supply of that or raw materials has come onto my radar.

      However, whitewash and related materials have significant fossil CO2 emission in production concerns.

      1. Whitewash is carbon-neutral; the CO2 driven off to make the lime is absorbed back as the whitewash cures. Meanwhile, I found the paper (10.1016/j.xcrp.2020.100221) and they’re using an acrylic binder for their paint (using DMF as the solvent, of all things), which is hardly environmentally friendly. Not to mention the paint is under-bound so it’s essentially interior primer and would likely fall apart in short order when used on a house.

        This sort of science-fair-project-as-journal-article is becoming worryingly common. They try to jazz it up by throwing in all sorts of graphs and using all types of million-dollar equipment, but in the end the content is totally worthless. I’m not joking, really; why DO we pay these people?

        1. Except for the large quantities of fuel you use to make it.

          >They try to jazz it up

          It’s just ordinary publication hype. Researchers investigate some interesting phenomenon and come up with results, and then they have to make up some greenwashing or “it’s for the disabled” excuse to the funders, who have to make excuses to their organizations and sources of income. It would be an interesting board meeting to see: “We’re paying millions to some dude to mix paint? Why?”

          Why: this is basic research, which can have applications elsewhere – just not here and now. Understanding the basic material properties and having a means to apply them is valuable knowledge, even if you will never actually put this stuff up on your roof. Otherwise it’s just armchair academia. The real value is that they’ve written the paper and shown people how to do it, so the next people can find the information and pick up the ball from there.

          For this case, the premise is laughable. The paint stops working immediately after the wind throws down a layer of dust on it. It only works because the reflectivity is so high that the absorption is less than the emission, but you only need to shift that by a couple percentage points and the balance tips the other way.

          1. More precisely: you do the hype BEFORE you get the results because you haven’t done the research yet.

            You only have to fib a little to win the next guy, so of course everyone makes fantastical claims just to get people interested. If you can add some magic incantations like, “climate change”, “public health”, “renewable energy”, etc. you’re that much better off in chances of getting funded, because the people who have the money don’t understand jack about the topics – otherwise they wouldn’t have hired your organization to do the research. This applies especially to government funding and charitable trusts who aren’t even in any related business and are just handing out money for tax and PR purposes.

            Honest funding applications that don’t promise you the moon from the sky don’t get the money. It’s been this way forever.

        2. I don’t understand your problem, this research has found a positive result. Is it the fact that they haven’t create a finished product suitable for all applications?
          Their research is showing that a house built in an area that ‘requires’ air conditioning to be cooled really should be painted with this kind of heat reflecting paint in the future, and whatever architectural changes are necessary to retain those heat reflecting properties for as long as possible should be made.

          1. I think the problem is the claims are bogus. It’s not net cooling in direct sunlight, just not quite as hot as some other things. So, maybe shave a few pennies off the electric bill, but not enough to get rid of the AC.

          2. My problem is that a fundamentally unworkable paint (high PVC, nasty solvent, non-durable pigment) is being marketed as a cure for global warming because it gives a 1-degree temperature difference in a poorly-designed experimental setup, and we’re supposed to accept this quality of research from public universities. Everyone knows white paint reflects light, and everyone knows chalk is white. There is no new data here, and the “researchers” knew this going in. Furthermore, this is part of a greater trend for research to use more and more expensive equipment (seriously, read the paper and tally it up) to achieve less and less practical results. If you watch the video, these guys can’t even use a paintbrush correctly, no joke.

            People need to give harsher criticism to this sort of thing.

          3. There are natural ways to get “air conditioning”, they are called “shadow of a tree”
            A tree has leafs in summer (therefore blocking the heat of the sun) and lacks leafs in winter (therefore allowing the heating from the sun).

            Also, the middle east region was home to many ancient civilisations that thrived in a hot climate, if instead of wasting resources we learnt from history, we could take some clues.
            In many places in Greece the houses are white, and not because of synthetic paint…

            The problem is that a marginal improvement over something ancient (handkerchief from coton to paper for instance) or something already good enough (iPhone 11 to 12, there’s no need to change phones every year if it wasn’t for software planned obsolescence…) is then scaled up by millions therefore creating actual issues.

            One air conditioner is not a problem, having tenths of millions of them is.

          4. @Scale – you are quite correct deciduous trees can be used to help in some areas. But you can also design the structure from the ground up to have cold wells that never see the sun to draw cooler air through the rest of the building passively through the day, slatted porch covers over windows so winter sun hits them but summer sun is blocked etc.

            @Anonymous While I don’t entirely disagree with your point, proving that binding chalk to the surface does work really quite well, while not a surprise is a step to perhaps creating a better future variation. Chalk is astonishingly abundant so being able to just ‘glue’ it to a surface and have it work could really work in the future. Ye ol’ whitewash type stuff is all well and good but you burn a great deal of energy to generate it, and it is no more durable… Just because we all can predict going in what the results will tend towards doesn’t mean we can skip doing the legwork – it might turn out to be really shockingly bad, or way way better than you could possible expect for any number of reasons.

            So the real thing to be annoyed at is the News circus that without ever understanding anything frequently takes legitimate science quantifying and documenting known effects as something huge and ground breaking so often. Its like the old https://xkcd.com/932/ situation, if you are educated enough you know what the news actually means its not even news worthy. But to the rest of the population it sure sounds good/bad/horrific etc..

          5. @Foldi-One
            But that’s the thing, gluing chalk to a surface is nearly as old as whitewash; it’s called gesso, and it’s never left as the final surface because it isn’t durable. It’s primer. The legwork has been done for hundreds of years; the only difference here is the use of an acrylic binder, but that defeats the whole point of an environmentally-friendly paint and probably isn’t even that much of a durability improvement. If they wanted a chalk paint with a high pigment concentration and an external binder, silicate paints are the best option, but again these have been a solved problem for decades. NASA uses them on spacecraft and the formulas are public knowledge.

            This is just a science fair project masquerading as research.

        3. ‘Anonymous’ said “Whitewash is carbon-neutral; the CO2 driven off to make the lime is absorbed back as the whitewash cures”. That’s true ONLY if the energy used to drive off the CO2 in the first place came from a carbon-neutral source. But usually that energy comes from burning fossil fuels, so it’s far from carbon-neutral.

      2. i’m not an expert on this stuff but i think you can make slaked lime by adding water to lime, which you can buy (i think for soil-modifying purposes) in big 60lb bags at most lumber yards. i don’t know how close to whitewash that really is…

        1. Nope, that’s exactly what whitewash is. People have been making it for millennia. It does have to be slaked lime though, not regular garden lime (which is just limestone). Of course, quicklime works too if you can find it. Slaked lime is the most convenient though.

  1. http://web.stanford.edu/group/fan/publication/Raman_Nature_515_540_2014.pdf For anyone wanting a better understanding of how it works.

    I’m no expert, but I have strong doubts about the claims in the article. For one, the paper I linked above went to much greater lengths to achieve net cooling effect. I don’t believe that they could have just used lime instead and gotten similar results.

    Second, when they are specifically indicating that the material has lower emissivity in the IR range, is it reasonable to use an IR camera to measure the surface temperature? I wouldn’t think so, but maybe someone here knows better than I do.

    Not to say it wouldn’t help with the electric bill a little bit, but reverse global warming? Not a chance.

    1. It would be interesting to see the results from a thermocouple embedded in the paint.

      It might not reverse global warming (alright, it definitely won’t reverse global warming) but it would be interesting to consider how the heat bubble of a large city would be changed by using paints like this. I suppose the majority of the city heating effect is the dark paved roads, and we wouldn’t want to make them white until no drivers have to look at them.

      1. I didn’t read the whole paper, but apparently that is what they did for the actual results. With the “ambient” temperature being measured by a thermocouple inside a box in the sun. So it’s only a couple degrees cooler than whatever the box was made of, and probably still significantly hotter than the actual air temperature. I’d be very surprised if a reasonable comparison to aluminum foil or another highly reflective material fared well.

    2. Your IR camera question is a really good one. The peak emission wavelengths for the kind of temperatures in this usecase would be around 8-15um. From their graph that area seems reasonably similar for the two materials.

      1. Except that it is. Did you not see the graph? The blue areas represent the return radiation from atmospheric gases, where the paint works exactly the same as the comparison, and it does worse than the commercial paint in the shorter IR range where the atmosphere is transparent.

    1. The more I look into this paper the worse it gets. They used the infrared camera results as clickbait, but the actual results they got via a pair of thermocouples looks to be just a degree or two celsius, and that’s because they “shaded” (enclosed) the reference thermocouple in a box out in the sun. Meaning the reference thermocouple isn’t just measuring the ambient temperature, it’s also measuring the temperature of the (presumably unpainted) box.

      Fake science. Defund Purdue.

    2. I was wondering the exact same thing. They should produce a significantly sized panel of it and measure the temperature from below to a reference panel painted in “commercial white”. Until I have seen that I bet that there is an effect, but not as significant as they make it appear to be.

  2. And when this new paint is chemically changed by acid rain (say sulphur dioxide based sulphuric acid), how well does calcium sulphate (plaster of Paris) compare with calcium carbonate at reflecting sunlight ?

    1. It would mainly dissolve on the next rain so you’ll end up with no paint anymore and a huge albedo. The real composition of their paint is kept secret (not described in their paper), but it’s not whitewash only else it wouldn’t hold the time and weather. Paint are a lot more complex than just pigments, IMHO. I don’t know if the whitest paint is only 80% reflective but if it’s the case, it’s very poor.

  3. irrespective of how good the paint is at reflecting IR emissions in the appropriate range to make a significant impact, as long as designers/ housing estate covenants keep specifying dark roofs its really not going to make any difference.

  4. So if this is passively reflecting IR light would this not make my house even colder in the winter? Would I not just be shifting my bill from running AC to running a heater? I would assume as the temperature gets colder the difference this brings is reduced because there is less sunlight to reflect but I wonder what the net overall gain is. I’m also curious about weather wear as others have pointed out.

  5. Seems useful but should be used with care.
    It takes energy to warm a place also, if used incorrectly it will be cooling things all the time.
    For example one doesn’t want the building radiating dutifully all the energy being pumped into it to maintain a constant temperature inside. So if used improperly the paint could also cause more energy consumption. Another way to look at it, the problem was changed, not solved per sea.

  6. So, they mean to tell home owners that they can paint their house (roof, whatever) any color they want as long as it’s white? Using their specially formulated paint in their particular shade of white (all under patient and legally licensed, of course)? Yeah… No. Even if I didn’t have reservations concerning the validity of man-made global climate change, the answer would still be no.

    If the plan is to use it on large office buildings and the like, to eliminate AC, then they need to have another plan for circulating air inside one of those monsters. That’s mostly what the AC unit on top of these buildings is used for. Big sealed building, a large number of employees, no air circulation… Good luck with that. :D

  7. I remember reading something about a building that was super-efficient in repelling sunlight and staying cool, due to it’s special reflective windows and paint.

    Only to find out that the surrounding buildings, the surroundings in general, and especially the traffic, were having serious problems with the reflections from that building. So they had to paint the building a different color, and think up something to cover the windows (because replacing them was going to cost way more than they could afford at that point).

    So I am not convinced too much about the practicalities of this paint…

    1. Basically it’s better to absorb all of the energy, lead it away, and store it for later use. And we already have things that can do exactly that: solar panels.

      They’d better look into solar panel paint. As far as I know, nanotechnology is very promising in this field.

    2. Oh.. it get better they some Architect made a concave shaped building (litterally a solar concentrator) as in it melted cars across the street. You can google something like “mirrored building kills trees and melts cars.”

      Humans are very stupid to be honest.

      The direction the house is facing matters a lot for the comfort of occupants.

      Harvesting it would be ideal.. using it in combination with a cool north side. One could use the heat to power a sterling engine.

      It only requires 4 degrees of temperature difference.

      1. Makes no sense why people want to make such a big deal about re-inventing the wheel.

        Fact is they use lime/calcium carbonate to paint the bottoms of trees to make give the high visibility all over europe..

        Until the EU said “that’s bad”.

        Of course people will be “intrested” because they created the “hype”

        Personally I’m curious what happened to that flexible translucent solar panel material?

        And the designs of using a so called 3D lattice framework with mirrors to increase capture efficiency?

        Either tech is being buried or it was bull in the first place. This particular story is bull.

  8. Thin foil would probably do a better job. The problem with either option are esthetics, cleaning, and cost. The cost of roofing materials is very inexpensive. If you increase the cost by multiples, it will be very hard to justify, even with lower electricity bills. Electricity is paid by the occupant, but the roof is paid by the entity that builds the home.

  9. Someone here in the art community here has meme-ed us LALA, LAfayette-west LAfayette. Cue the Theremin music, horn stabs, and strident strings! Or the germanichse “urdunaperversity, is local way of putting it. We lost bar time when Purdue opened on the east side as well.

  10. But you seem to be forgetting that in colder climates the effects of a dark roof help reduce heating costs. What we really need is a temperature dependent paint, one that turns white above about white above 20C and black below 15C, paint it once and it’s good all year long.

  11. Reducing urban heat islands is a great and old idea, just take a look at the communities on islands in Mediterranean, however it also highlights how covering large areas of Earth’s surface with dark solar panels is harmful, as >70% of the light energy hitting them is downconverted to heat.

      1. Yes Mike what I pointed out is correct as most large scale solar PV installations are built over land that has a lighter albedo, i.e. it reflects more light back toward space without downconversion. Why did you even need to ask, you can just go and look that up! You would need to have your solar PV arrays over the deep ocean to avoid that albedo problem as the ocean has the closest match r.e. absorbance. Then you get cooling for free too, so they run more efficiently, however the total cost of installation blows out a lot. You know how it is, there is not much you can’t fix with engineering if somebody is prepared to pay for it, however in this case the costs would completely destroy the myth of solar derived energy being cheaper than other sources. How about we just wait for fusion reactors huh? As for the whole IR and greenhouse gases thing, that is a mirage to fool people who don’t even realise how many separe thermodynamic processes are in operation in a real atmosphere. Amongst all of those I find that the way that the top of the atmosphere and the waves deep under the ocean surface are gravitationally linked is fascinating. You can look that up too! :-)

  12. Plus, in 2050 when the earth is much cooler you can paint over this stuff with black paint because you want to hold onto the sun’s heat instead of reflecting it back into space.

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