Nature’s blueprint: New power-free bio-inspired hydrogel cools buildings in summer, warms them in winter

• Researchers from KAIST and Seoul National University developed a hydrogel material that regulates temperature without electricity.
• The bio-inspired design mimics poplar leaves that curl to reflect sunlight in heat and release warmth at night.
• The material autonomously switches between four heating and cooling modes based on environmental conditions.
• Outdoor tests showed temperatures up to 6.7°F cooler in summer and 6.3°F warmer in winter compared to conventional materials.
• Simulations predict annual energy savings of 153 megajoules per square meter across seven global climate zones.

As energy costs continue to climb, a breakthrough from South Korea offers a glimpse of a smarter, more natural way to keep our living spaces comfortable. Researchers from the Korea Advanced Institute of Science and Technology (KAIST) and Seoul National University have developed a revolutionary material that manages temperature without consuming a single watt of electricity. This innovative hydrogel, inspired by the humble poplar leaf, autonomously switches between cooling and heating modes, promising a future where buildings can self-regulate their climate by emulating the intelligence of the natural world.

The research, published in the journal Advanced Materials, takes its cue from the survival strategy of the white poplar tree (Populus alba). When faced with hot and dry conditions, the poplar leaf curls to expose its silvery-white underside, reflecting sunlight to stay cool. At night, moisture that condenses on the leaf surface releases latent heat, providing a protective warmth against frost. This sophisticated, passive response to environmental changes served as the perfect model for a new kind of thermal management.

The KAIST team, led by Professor Young Min Song of the School of Electrical Engineering, in collaboration with Professor Dae-Hyeong Kim’s team at Seoul National University, engineered a flexible “Latent-Radiative Thermostat (LRT)” to replicate this natural process. “This research is significant as it technically reproduced nature’s intelligent thermal regulation strategy, presenting a thermal management device that self-adapts to seasonal and climate changes,” Professor Song said in a statement.

How the material works

The core of the LRT is a hydrogel—a gel-like substance made from polyacrylamide—that is integrated with two key components: lithium ions and hydroxypropyl cellulose (HPC). Each plays a critical role in this power-free system. The lithium ions are responsible for managing moisture, absorbing and condensing it from the air to regulate latent heat. The HPC, however, is the star of the show, changing its state based on temperature.

When the surrounding temperature rises, the HPC molecules within the hydrogel aggregate, causing the entire material to become opaque. This opaqueness reflects sunlight, providing a cooling effect. Simultaneously, any moisture held within the hydrogel can evaporate, creating an additional evaporative cooling mechanism, much like sweat cooling human skin.

A true four-mode thermostat

This design allows the material to operate in four distinct modes without any external power source. In cold, nighttime conditions, it absorbs and condenses atmospheric moisture, releasing heat to maintain warmth. On cold but sunny days, it remains transparent, allowing sunlight to pass through and be absorbed by the trapped moisture, which then generates a heating effect.

In hot, dry environments, the internal moisture evaporates for powerful cooling. Under the most intense summer conditions with strong sunlight, the HPC turns opaque to reflect solar radiation while evaporative cooling works in concert to actively lower the temperature. It is a fully autonomous system that responds to the environment in real time.

The potential impact of this technology is substantial. In outdoor tests, the LRT maintained temperatures up to 3.7 degrees Celsius cooler (6.7 degrees Fahrenheit) in the summer and up to 3.5 degrees Celsius (6.3 degrees Fahrenheit) warmer in the winter compared to conventional cooling materials. Simulations across seven different global climate zones predicted annual energy savings of up to 153 megajoules per square meter compared to standard roof coatings.

This innovation arrives at a critical juncture. As energy grids are strained by extreme weather and the push for sustainability grows louder, solutions that decouple comfort from massive electricity consumption are more valuable than ever. This bio-inspired material demonstrates that the most advanced technologies are often those that humbly learn from the world around us, offering a path toward a more resilient and energy-independent future.

Sources for this article include:

TechXplore.com

DongaScience.com

Chosun.com