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Yes, you can make a simple cooling-paint experiment by mixing calcium carbonate powder into outdoor white paint. But it is not a proven homemade cooling recipe: in a small 2026 outdoor comparison, the mixtures stayed close to ordinary white paint and showed no consistent cooling improvement. White paint can reflect sunlight, but looking white alone does not establish the solar reflectance and infrared emission needed for radiative cooling.
What you can make at home—and what the evidence shows
The most directly tested DIY approach is to add calcium carbonate (CaCO₃) powder to commercial outdoor white paint. Advik Gujrati’s May 12, 2026 article in the National High School Journal of Science compared paint containing 45% and 65% calcium carbonate by mass with the unmodified white-paint control. It also tested different ways of applying the 65% mixture and included uncoated aluminium panels. The outdoor comparison ran for two weeks, with one panel per condition per week, and used an infrared thermometer to record surface temperature. Read the study.
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During the strongest heating, uncoated aluminium peaked approximately 10–12 °C hotter than regular white paint; the calcium-carbonate panels were typically within ±1 °C of the white-paint control. The study found no consistent separation between the two additive levels or among application methods. These results come from a small comparison, and the study did not independently characterize reflectance, emissivity or coating microstructure. They do not prove every calcium-carbonate formulation is ineffective, but they do show that simply adding a common powder to already-good white paint is not a demonstrated shortcut to a large cooling effect.
If you want to reproduce the comparison, the tested mass fractions are useful reference points, not a validated recipe. The study does not establish a reliable mixture for cooling a building, and it does not show that the homemade coating can cool below ambient air temperature.
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Why ordinary white paint is not automatically cooling paint
Visible whiteness is not enough to predict radiative-cooling performance. A daytime radiative-cooling surface needs to reflect incoming sunlight across the solar spectrum while efficiently emitting heat as infrared radiation, particularly through the part of the atmosphere that lets that radiation escape toward the sky. A surface can look white without having the necessary combination of optical properties. The DIY study and a 2025 Nature Protocols evaluation procedure describe why appearance or a single temperature reading cannot establish those properties.
Formulation and processing matter: particle size and distribution, filler loading, binder, coating thickness and application method can all affect a coating. Engineered studies specify those choices rather than assuming that any white paint—or any powder added to it—will work.
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How engineered coatings differ from a paint-and-powder mix
Alumina and sodium methylsilicate
A 2025 Journal of Materials Chemistry C paper describes a water-based inorganic radiative-cooling coating made by adjusting the ratio of alumina particles to sodium methylsilicate adhesive. Its preparation mixes the materials with water, stirs for 30 minutes, sprays the mixture onto a substrate and dries it at indoor temperature; the research also uses a hydrophobic surface treatment. This is a defined materials formulation, not an everyday household-paint recipe. See the paper.
TPU, barium sulfate and silica
A separate 2025 study describes dispersing barium sulfate and hydrophobic silica powders in dimethylformamide (DMF), then adding thermoplastic polyurethane (TPU) and spraying the coating. Its reflectance, emissivity and temperature results belong to that engineered composition and method, not to standard white paint. DMF handling is not a casual DIY activity. See the study.
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How to run a fair home comparison
A basic side-by-side panel test can show whether a mixture behaves differently from the paint it starts with. It cannot, by itself, establish radiative-cooling power. Keep the comparison simple and record what you do so the result is interpretable.
- Prepare three panels of the same material and size: one coated with the commercial white paint alone, one with the proposed mixture, and one left uncoated.
- Match orientation, coating coverage and drying time for the two painted panels. Record the base-paint mass, additive mass, mixing method and application method.
- Place the panels side by side outdoors so they share sunlight and weather. Record the time and conditions alongside surface-temperature readings over time.
- Use an infrared thermometer consistently on the same locations and surfaces. Treat its readings as a surface-temperature comparison, not a direct measurement of radiative-cooling power.
For stronger evidence, optical measurements and more controlled outdoor testing are needed. Wang, Pian and Ma’s Nature Protocols procedure, published online in 2025 and appearing in volume 2026, describes solar measurements over 0.3–2.5 μm and infrared measurements over 2.5–20 μm. Its outdoor workflow accounts for insulation, radiation shielding, humidity, sunlight, wind and ambient temperature; typical durations are seven days outdoors and one day indoors. The authors note that comparisons are difficult without standardized, transparent evaluation. Read the protocol.
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What specialist cooling paint claims—and how to read the numbers
SRI International describes its Self-Cooling Paint as a passive radiative-cooling product for sky-facing outdoor surfaces. The company says it combines high solar reflectance with high infrared emittance in the sky transparency window. SRI reports, based on its internal tests, cooling up to 5–8 °C below ambient air temperature and 10–15 °C below an uncoated surface, as well as daytime summer cooling power on the order of 100 W/m². Those are vendor-reported results, not measurements from the DIY calcium-carbonate comparison. SRI cautions: “Others may see results that vary from our internal tests — as with any coating, cooling performance varies based on the application and surrounding conditions, including weather.” See SRI’s product information.
SRI says the product is available by contacting the company. Its listed applications include electronics enclosures, aerospace and drones, power generation, textiles, architecture, tents, storage tanks and automotive use. The product page does not establish broad consumer retail availability.
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Keep the measurements distinct
When judging a cooling coating, separate the property being claimed from the way it was measured. Reflectance describes how much incoming radiation a surface sends back; emissivity describes how effectively it emits radiation. Surface temperature is not the same as indoor temperature, and neither measurement alone is cooling power. A vendor’s sub-ambient claim, an optical laboratory result and a small outdoor panel comparison are different kinds of evidence, so they should not be treated as directly interchangeable.
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