In a concrete building known as “the bunker,” researchers at PPG, a $24 billion company that makes paints, aimed torches at steel panels that were covered in a gray coating.

Paul Fenton, a PPG chemist and engineer, held up one panel after it had been blasted with flames. The paint had swelled from a millimeter thick into a black crust nearly 10 millimeters tall. That meant the coating had done its job: The thick crust had kept any fire from reaching the underlying steel and softening it.

“Just like a toasted marshmallow likes to expand,” said Mr. Fenton, who wore a lab coat and safety goggles over wire-frame glasses. The trapped air, he said, “keeps everything cold.”

The paint that Mr. Fenton showed off, called Steelguard 951, has become one of PPG’s flagship products for data centers — and its sales have boomed. As Microsoft, Google, Amazon and other tech giants have raced to build the computing sites powering the artificial intelligence frenzy, PPG’s business has also soared.