Whose idea was it to build our modern buildings out of glass? Floor to ceiling windows may provide a beautiful view but they force building owners and managers to install highly energy consuming heating and air-conditioning systems (HVAC) to regulate against sunlight or lack of. No wonder buildings account for as much as 40% of total energy consumption.

Before the emergence of plate glass in the 1930s, buildings tended to be constructed with thick walls and small windows, which while insulating well, did not allow for adequate ventilation and depended on interior daytime lighting. Now, as we move into a smart, energy-efficient era, our buildings’ outer layer, or skin, is due an upgrade. Some in the sector are looking to biology for an answer.

“What I propose is that our building skins should be more similar to human skin, and by doing so can be much more dynamic and responsive,” says Doris Kim Sung, a biologist-turned-architect and principal of dO|Su Studio Architecture as well as assistant professor at the University of Southern California. Underlining that, “merely by focusing on the effort of transforming mechanical systems into a more efficient prospect, we cannot do net-zero energy.”

This is not an entirely new idea; in fact we covered the concept more than a year ago in our article ‘Nature Provides Inspiration for Smart Building Façades.’ Suggesting that, “much like human skin, a building’s outer layer needs to be weatherproof, insulating and, ideally, maintain an attractive appearance. Also like a human skin, a building’s façade has the potential to provide essential sensory input, allow regulation of temperature and air circulation, adapt to its environment and derive important elements from the sun’s rays.”

Sung and her team have been constructing windows, walls, and building components with metals, which curl when heated, otherwise known as thermobimetals. These are composite alloys where two types of metal are slammed together with an industrial press, permanently fusing them. One material expands at a faster rate when heated than the other. As the first material expands, it’s held in place by the slower expanding material, and it begins to curl.

It is the first time such materials have been used in architecture and, rather than just mimicking human skin, thermobimetals use in buildings was also inspired by the breathing system of a grasshopper. “Grasshoppers have a different kind of breathing system. They breathe through holes in their sides called spiracles, and they bring the air through and it moves through their system to cool them down, and so in this project, I'm trying to look at how we can consider that in architecture too, how we can bring air through holes in the sides of a building,” Sung explained during a TED talk.

Despite her pioneering work, it is still early days for thermobimetals in architecture, Sung’s research-based practice, located in Rolling Hills, California, near Los Angeles, is still operating primarily from grant money. “We don’t have clients,” Sung says as she seeks to turn this little-known material into a dynamic and transformative building element. “We don’t know exactly what it is until we get there,” she says.

Thermobimetal strips, disks or spirals, are commonly used as a measurement and control system within thermostats and as components in mechatronic systems for electrical controls. The few architectural applications that have been documented include, automatic ventilation flaps and self-closing fire protection flaps for greenhouses, but Sung is the first to develop the material for building skins.

Some have already criticized Sung’s work as overly simple and determined, considering this basic, binary reaction, but Sung points out that there are more variables at play. “It’s actually super complicated,” she says. There’s the curl temperature and amount, as well as the geometry of the cut, which can turn a curl into a twist for example. “Our difficulty is that we have to design something [that goes] from the closed position to the extreme open position and for the thousands of positions in between because we can’t always say it’s going to be 95 degrees that day.”

Sung’s most commercially promising research focuses on a window system that places sheets of thermobimetal between dual-paneled glass. The metal sheets remain parallel to the sun’s angle at cooler temperatures, allowing in ample sunlight and heat. As the temperature rises, the metal sheets begin to curl, ultimately blocking out the sun.

Such environmentally reactive systems transcend the typically binary division of passive versus active sustainable building systems. Sustainable buildings must first prioritize static, passive elements (like quality insulation) before looking to more expensive, active energy generation and climate control systems.

Thermobimetals act like passive systems that require no energy or attention to use once installed, but also like active systems that respond to their climate and environment. Sung calls it a “passive-active system.”

The emergence of smart materials has elevated interest in utilizing unconventional building systems to serve our need for sustainable and energy-efficient structures. Such buildings can be more sensitive to the environment and its inhabitants, raising the level of a structures’ effectiveness while altering our perception of enclosure. It’s a reminder that smart systems don’t always need to be digital.

Bio-mimicry is allowing us to harness the power of nature in a much more natural way, while maintaining comfort and responsiveness that modern society demands. “If we're really smart, we'll design building skin to sweat, to have goosebumps, to be waterproof,” Sung concludes. "It's a different way to see architecture. We're on the cusp of something new."