Austrian researchers 3D-printed porous ceramic cubes for passive cooling; one water-filled prototype cooled nearby air by nearly 7°C without electricity

It’s getting harder to escape the summer heat, and air conditioning might not always be the answer. Air conditioners cost money, eat up electricity, and blow warm air right back onto the street. So a team at Graz University of Technology in Austria decided to look back for an answer and then print it forward with a 3D printer. They constructed a wall of tiny porous ceramic cubes. Fill one cube with water, and the air around it cools by about 7°C. No plug, no compressor, and no electricity use during operation.

It sounds simple, but the underlying science has long been studied and is now getting a modern upgrade.

How a block of clay cools the air


The trick is called evaporative cooling, and humans have used it for centuries. Consider a clay water pot that remains cool even on a hot, humid afternoon. As the water moves through the clay and evaporates off the surface, it pulls heat away from whatever it is touching. That is the same principle behind old wind towers used in hot, dry regions.

The TU Graz group, headed by architect Milena Stavrić, recreated the ancient cooling method with 3D printing technology. Every cube is about 23 centimeters long in all dimensions and made from a unique mix of clay. The cube is also fired at low temperatures to preserve the material’s high porosity so it can absorb water through capillary action.

Why the shape is as important as the material

What makes these cubes special is not only their composition but also the internal geometry. These cubes have been designed by using a mathematics-based model called triply periodic minimal surfaces, or TPMS, which can incorporate a huge amount of surface area in a small volume by using relatively less material. This increases the evaporative capacity and cooling effect of the device. More surface area allows more water to evaporate, which increases cooling.

The water entered the cube and was evenly distributed throughout the interior. The heat from the air was drawn out of it as it evaporated, just like sweat on a hot day cools your skin.. In an experiment conducted indoors in a hot attic, the team recorded a reduction of almost 7°C around a cube filled with water.

That passive cooling effect is well established in building science. In a 2010 study published in the journal Building and Environment, porous ceramic walls with high water-absorbing ability were tested and found to be able to meaningfully lower surface and air temperatures in outdoor and semi-outdoor spaces without any mechanical cooling. This same well-documented principle is what the TU Graz cubes rely on, although with a more complicated, 3D-printed internal geometry.

Fungi join the experiment

The TU Graz researchers aren’t stopping at clay and water. They blend fungus with sawdust, which goes into the mix of clay before it is printed using both as intentional pore-forming agents. As the mix is fired, the fungal threads and sawdust burn away, exactly as intended, leaving behind a further web of tiny pores. This could mean more room in the ceramic for water to flow through, possibly making the cooling effect last longer.

They are also experimenting with sediment dredged from Lake Neusiedl, a shallow lake in Austria that must be dredged regularly to prevent it from silting up. Instead of throwing the sediment away as waste, the team wants to turn it into a usable, sustainable building material using 3D printing.

Why this actually matters for cities

Cities are getting hotter, and it’s not just climate change. Concrete, asphalt and glass absorb heat and release it back into the air long after sunset, an effect researchers call the urban heat island effect. As cities get bigger, so do heat islands, which can worsen extreme heat exposure, the US Environmental Protection Agency notes.

Air conditioning is not a fair solution for all spaces. It is expensive to install, expensive to operate, and is not available in many public places such as parks, courtyards and waiting areas. That gap could be filled by a passive ceramic wall cooled by water and evaporation. Stavric and her team envision uses in homes, offices, schools and outdoor public spaces, particularly in crowded urban centres where trees cannot offer sufficient shade or cooling.

What comes next

The concept has already expanded beyond the lab. These ceramic cubes can now be seen in a free-standing two-by-two-meter demonstration wall on the TU Graz campus in Graz and as a prototype at the Museum of Perception in the city. Anyone interested can simply go and feel the cooling effect.

For now, the project remains a proof of concept, receiving financial backing from Austria Wirtschaftsservice GmbH. However, it hints at a greater concept: sometimes the most efficient cooling technology of the future is one that was already sitting in clay pots thousands of years ago, just waiting for a 3D printer to unlock its full potential.