Comedian Steven Wright once famously quipped, "It's a small world, but I wouldn't want to paint it."
Well, mechanical engineering students at Purdue University apparently saw that as a challenge three years ago, and under the guidance of Prof. Xuilin Ruan, set about developing the whitest paint in the world. Why? Because ultra-reflective white paint has the potential to keep the planet MUCH cooler.
In 2022, the Guinness Book of World Records officially certified their work as the whitest paint in the world. It’s an ultra-white paint containing barium sulphate nanoparticles that give it 98.1% reflectance (R=0.981).
By comparison, most white paints have R=0.80 and an emittance of 0.90, which result in a Solar Reflectance Index (SRI) of 100, when calculated according to ASTM E1980-11(2019). Using the same calculation, the Purdue paint has SRI>124 (SRI values for most materials range from 0-100).
To put that into perspective, for a new construction project, LEED awards maximum points for heat island reduction for roofs with SRI≥82 and non-roof surfaces with R≥0.33.
So Purdue’s white paint could be a game-changer. According to the Guinness citation, using the paint to cover a roof area of about 1,000 sq ft (93 m2), would result in a “cooling power” of as much as 10 kW. Since most residential air conditioners in use range from 1.5 to 5 tons (5 to 17.5 kW), that’s pretty significant.
According to scientists, painting jusy 1% of the Earth's surface would completely reverse global warming. Since the paint also has high emissivity (its ability to emit infrared energy), roofs painted with the ultra-shite paint would emit more heat than they absorb, and would be cooler than the surrounding ambient temperature by as much as 8 deg F. (4.5 deg C.).
Of course, the downside of the Purdue paint is the thickness of the coating required to obtain that performance: approximately 400 μm (0.02 in), rendering it largely impractical for use on surfaces other than roofs – just imagine the glare from using it on hardscape!
So, recognizing that problem, the same researchers spent the next year developing a thinner, lighter paint for weight-sensitive applications. That paint is almost as white as the original – R=0.979 – and requires only 150 μm thickness (0.006 in) and weighs just 0.029 g/cm2 (0.0004 lb/in2). That makes it suitable for planes, trains, cars, trucks, and a myriad of other applications where weight is critical.
According to the latest information on the web, the paint will be commercially available “once further testing concludes and it meets all regulatory approval criteria.”
Looking back, maybe Steven Wright was wrong. We do want to paint the world now!
##########