Super-cool cement could stop buildings trapping heat inside
A new formulation of cement reflects and emits heat more effectively than normal Portland cement, so it stays much cooler on a hot day
By Alex Wilkins
20 August 2025
Concrete buildings absorb heat in hot weather
Panther Media Global/Alamy
Cement that can cool itself by reflecting light on the outside and releasing heat from its surface could help buildings stay comfortable without needing air conditioning.
Normal cement tends to absorb infrared radiation from the sun and store it as heat, which can increase the temperature inside cement buildings as well as that of the surrounding air.
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So Fengyin Du, then at Southeast University in Nanjing, China, and her colleagues decided to address this by creating a cement in which tiny reflective crystals of a mineral called ettringite collect on the surface.
The team’s cement emits infrared light from its surface, rather than storing it, and so loses heat quickly. “It works like a mirror and a radiator, so it can reflect sunlight away and send heat out into the sky, so a building can stay cooler without any air conditioning or electricity,” says Du.
To make it, the researchers first produce tiny pellets from common minerals like limestone and gypsum. These are ground to dust and mixed with water before being poured into a silicone mould covered in small holes. Air bubbles passing through the holes create slight depressions in the cement’s surface, where the reflective ettringite crystals can then grow, while an aluminium-rich gel in the set cement lets infrared light pass through the material.
