Published on 11 Oct 2021

Keeping the heat out

NTU researchers develop an energy-saving window that is able to regulate the temperature of buildings.

Energy saving liquid window

Windows are the least energy-efficient features of buildings, losing heat during cold weather while allowing heat to enter in warm weather. Buildings with windows require large amounts of energy for heating or cooling, adding significantly to the environmental footprint of cities.

Using a hydrogel-based liquid confined between two glass panels, a team of researchers from Singapore and China led by Dr Long Yi of NTU’s School of Materials Science and Engineering invented a window that is able to regulate the temperature of buildings.

During the hottest part of the day, the liquid absorbs heat and turns opaque, blocking sunlight and preventing the
building from heating up. At night, the liquid gradually cools and releases heat, thereby returning to its original clear

state. In colder environments, the window remains transparent throughout the day, allowing sunlight to enter and warm up the building.

“In our tests, the windows were able to reduce the energy consumption of buildings typically used for cooling,

ventilation and air-conditioning by almost 50%,” says Dr Long.

According to the researchers, the windows are also able to reduce ambient noise with about 15% higher efficiency than normal double-glazed windows.

The study “Liquid thermo-responsive smart window derived from hydrogel” was published in Joule (2020). DOI: 10.1016/j.joule.2020.09.001. You can watch a video on the research here:,

The article appeared first in NTU's research & innovation magazine Pushing Frontiers (issue #19February 2021).