Precipitated barium sulfate · M-Series

The filler that decides whether your cooling paint actually cools.

A passive radiative cooling coating has to do two jobs at once: bounce back nearly all the sunlight that hits it, and let the heat underneath escape through the 8–13 µm sky window. Barium sulfate is one of the few white minerals that does both. But only if the particle size, the purity and the sulfur level are right - and that is a manufacturing question, not a formulation question.

Ambition M-Series is precipitated barium sulfate built specifically for that job: D50 tuned across 0.7, 1.0 and 1.5 µm, 98% whiteness, 11–13 g/100g oil absorption, and a barium carbonate process route that leaves no free sulfur and no soluble salt by-product behind.
 

Get 1 kg free samples + TDS

 

 

80,000

tons / year - inorganic powders

60,000

tons / year - additive masterbatch

200%+

specialists & engineers

100+

batch-to-batch QC checked

Where your coating has to win：

Two wavelength regions, two opposite requirements. Everything below on this page is about hitting both with one filler.

Why formulators moved off titanium dioxide

TiO₂ is the reflex answer for a white coating, and it is the wrong answer for a cooling one. Rutile's band gap sits around 3.0 eV, so it absorbs in the UV and near-UV - precisely where solar irradiance is still strong. Worse, TiO₂'s high refractive index means it absorbs meaningfully in the near-IR tail. You get a paint that looks brilliantly white to the eye and still heats up in the sun.

Barium sulfate does not have that problem. Its band gap is close to 6 eV, which pushes absorption out of the solar spectrum entirely, and its lattice has a phonon resonance near 9 µm - sitting inside the atmospheric window, where the mid-IR heat your roof radiates can escape to the cold of deep space rather than bouncing back off the atmosphere. That is the pairing the Purdue research team exploited when their BaSO₄-acrylic paint reached 98.1% solar reflectance and 0.95 sky-window emissivity, holding more than 4.5 °C below ambient in daylight field tests.

Those figures describe a laboratory formulation at roughly 60% pigment volume concentration - they are the physics ceiling for the chemistry, not a claim about any single powder. What a supplier controls is how close your formulation can get to that ceiling.

One particle size cannot cover the solar band

Mie scattering efficiency peaks when particle diameter is comparable to the wavelength being scattered. A mono-sized grade scatters one slice of the spectrum well and leaves a hole at the blue end or the near-IR end. The literature is consistent on this: broad, deliberate size distribution is what carries solar reflectance past 95%. M-Series is supplied at three D50 points so you can build that distribution instead of hoping for it

Free sulfur is a process defect, not a spec line

Most Chinese precipitated barium sulfate is made by the black-ash route: barite reduced with carbon to barium sulfide, then reprecipitated. It is cheap, and it leaves traces of elemental sulfur and soluble salts. In a cooling coating exposed to UV for a decade, that residue is what drives yellowing, reflectance drift and blistering on metal substrates. We use the barium carbonate–sulfuric acid route instead. No sulfide intermediate, no free sulfur, no water-soluble salt by-product.

Three grades, built to be blended

Pick one for a straightforward cool-roof topcoat. Blend two or three when you are chasing reflectance in the last few percent, where the return on tuning the size distribution is largest.

Oil absorption per ASTM D281 equivalent. Dispersibility measured on a Hegman gauge. Full TDS with sieve residue, moisture, soluble salts, BaSO₄ assay and heavy-metal limits is issued with samples. Custom D50 and surface treatment available on development lots.

Same resin, same loading, same grind. One variable.

We ran M-700 against a competitor's precipitated barium sulfate in an identical waterborne acrylic system at 65% loading, ground to ≤25 µm fineness. Nothing else changed.

Read the viscosity line before the color line. The 35% drop from 1053 to 686 cps at identical solids is the number a formulator can spend. It means you can push pigment volume concentration higher before the paint stops being sprayable - and in radiative cooling, PVC is the lever that moves solar reflectance. A filler with high oil demand caps your PVC and caps your cooling with it.

The color result follows from the same cause. At 65% loading, a filler that agglomerates loses hiding and drops L* off a cliff. M-700's 90.28 whiteness against 38.27 is not a marginal improvement in a pigment; it is the difference between a functioning reflective layer and a grey one.

 Internal application-lab data, Yunfu, 2026. Competitor sample sourced commercially and unidentified for legal reasons; we will disclose the grade class under NDA. Results will shift with your resin, dispersant package and grind - which is why we run your system, not ours, during evaluation.

The part of the decision that isn't chemistry

A filler that performs in a 200 g lab batch and drifts across production lots is worse than a mediocre filler that never moves. If you are qualifying a new barium sulfate supplier, the honest questions are about the plant, not the powder.

Yunfu Hongzhi New Materials was founded in 2017 and operates in the Yunfu Circular Economy Industrial Park, Guangdong. Thirteen production lines, roughly 80,000 t/yr of inorganic powder and 60,000 t/yr of functional masterbatch. Certified to ISO 9001 and ISO 14001, recognized as a National High-Tech Enterprise and a Guangdong "specialized and sophisticated" (SRDI) enterprise, with a provincial engineering technology research center on site.

Our technical team took part in drafting HG/T 2774-2023, the Chinese chemical industry standard for modified ultrafine precipitated barium sulfate - the test methods your COA is written against. We are also one of a small number of producers worldwide running pigment-grade zinc sulfide at industrial scale, which is the same particle-engineering problem in a different chemistry. You'll find us at CHINACOAT and CHINAPLAS every year; come argue with the data in person.

How evaluation actually runs

FAQ

 

 

01.Why barium sulfate instead of TiO₂ in a radiative cooling paint?

TiO₂'s ~3.0 eV band gap means it absorbs in the UV and near-UV, right where solar irradiance is strong - so the paint looks white and still heats. BaSO₄'s band gap is near 6 eV, keeping it non-absorbing across the whole solar band, and its phonon resonance near 9 µm sits inside the atmospheric window. That is why ultrawhite research paints moved to BaSO₄. Many production formulas keep a small TiO₂ fraction for hiding and use BaSO₄ for the reflective work.

02.What particle size should I use?

No single size scatters the whole solar band - scattering peaks near a diameter comparable to the wavelength, so a mono-sized grade leaves a hole at the blue end or the near-IR end. Broad distribution is the published answer. Start with M-1000 as a baseline, then add M-700 if you're losing the blue end or M-1500 if the curve is dropping past 2 µm. We'll suggest a starting ratio for your resin.

03.How much cooling can I actually promise my customer?

Be careful here. Published lab systems reach 98.1% solar reflectance and more than 4.5 °C sub-ambient. Real roofs, real humidity and real dirt do less. A realistic surface-temperature reduction from a well-formulated M-Series coating is 3–5 °C, with 10–30 °C achievable against an uncoated dark substrate under clear, dry, high-irradiance conditions. Humidity closes the sky window; a coating that performs in Arizona will underperform in Florida. Any supplier quoting one number for all climates is selling, not measuring.

04.Which standards will my finished coating be tested against? 

In the US, expect solar reflectance by ASTM E903 or C1549, thermal emittance by ASTM C1371, and Solar Reflectance Index calculated per ASTM E1980 - plus three-year aged values if you want a CRRC listing or ENERGY STAR. We supply the filler and the filler's data; the listing is earned by the finished coating. We can tell you which grade combination our customers used to get there.

05.Is barium sulfate a regulatory problem?

No. BaSO₄ is among the least soluble barium salts, which is why it is the barium form used in consumer coatings and as a medical radiocontrast agent. It is not hazardous cargo. What matters is soluble barium content, controlled by process route and washing and reported on the COA - another reason the barium carbonate route beats the black-ash route. GHS-format SDS ships with every order; REACH and RoHS documentation available on request.

06.Do you supply samples, and what's the MOQ?

1 kg lab samples of each grade are free, with documents, by courier. A paid 25 kg trial lot comes from production stock. Production MOQ is one pallet (1,000 kg); most cooling-coating customers move to FCL within two orders. Tell us your resin system and target reflectance in the first message and we'll skip a round trip.