As yet another heatwave reignites debate over air conditioning energy use, scientists and engineers are hard at work in their laboratories developing far more efficient passive cooling solutions for architecture. And some are innovating by tapping into designs sixty million years in the making.

Just like other biomimetic technologies covered on this site, researchers have turned to structures found in the animal kingdom, specifically elephants. In this feature article, we explore the inner workings of a new cement that keeps buildings cool through a network of pores inspired by the skin of these mammals.

African elephants face extreme temperatures in arid environments daily without the ability to sweat like humans. Their secret to keeping cool is etched right into their skin, thanks to a dense network of microscopic cracks and channels that hold water and mud. Resembling parched earth during a drought, this structure multiplies the surface area in contact with the air and draws moisture across the entire body via capillary action, optimizing evaporative cooling.

A multidisciplinary team of researchers from the University of Pennsylvania has brought this physiological mechanism into construction materials. By replicating the wrinkled surface of elephant skin on porous cement tiles, they engineered a facade cladding that behaves like a “living skin” for buildings. This is the core of bioclimatic architecture.

The principle behind this breakthrough pairs capillary action with controlled evaporation. Rather than having a conventional smooth surface, the cement tiles feature a geometric pattern of criss-crossing microchannels that absorb rainwater and nighttime dew. Its key properties include.

1. Capillary wicking: The network of microcracks spreads water evenly across the entire tile surface, preventing localized pooling and speeding up evaporation rates.
2. Expanded exchange surface: The textured surface inspired by elephant skin increases the surface area exposed to the air without adding bulk to the tile, maximizing heat dissipation.
3. Evaporative cooling: As moisture trapped in the cement evaporates under solar radiation, it draws thermal energy away from the facade. This process cools the building's interior naturally. It relies, after all, on the exact same mechanism traditional earthenware pitchers use to keep water cool in summer.

Laboratory tests show this biomimetic cladding lowers external wall surface temperatures by several degrees. “A passive, bio-inspired cooling facade like this could lower surface temperatures by 10–20°F (6–11°C) compared to traditional stucco,” explains Professor Shu Yang, one of the researchers behind the project. This thermal difference stems heat transfer into living spaces and lowers demand for artificial air conditioning during peak hours.

Unlike conventional air conditioning units that consume electricity and pump hot air outside, this material acts as a passive cooling solution that runs on zero electricity during operation. Integrating it into urban settings could offer a powerful tool to counter the urban heat island effect, an issue aggravated by the heavy concentration of asphalt and dark surfaces in cities.

• Egyptian blue: Based on calcium copper silicate, this vivid blue pigment is considered history's first synthetic pigment. Research from the Lawrence Berkeley National Laboratory reveals that Egyptian blue emits nearly 100% of absorbed solar photons as infrared radiation. This yields an energy efficiency of 70%, since infrared light contains less energy than visible light, while the remaining radiation dissipates as heat—a process known as passive radiative cooling.
• Shape-memory materials: Another approach uses shape-memory materials that adjust their behavior to environmental conditions. Inspired by the way pinecones open and close their scales hygromorphically in response to humidity without consuming energy, researchers at the Technical University of Munich (TUM) have developed passive climate control and lighting systems for buildings. This biomimetic technology enables kinetic facades and smart louvers that automatically adapt to outdoor weather, optimizing ventilation and natural daylight.
• Cooling wood: A third strategy alters a material's composition to give it passive radiative cooling properties. This is the case with a new type of near-white wood. By stripping out the lignin in natural wood, researchers at the University of Maryland engineered it to emit mid-infrared radiation, the wavelength directed straight back into space to cool a building. It is also eight times stronger than conventional timber.

For more on materials with remarkable properties, take a look at our feature article on a bioplastic that mimics spider silk or phase-change materials that store and release heat and cold on demand.

Source:

• TechXplore