Window shades respond to weather

No person or electricity is necessary to open and close these window shades. On an early afternoon in March 2023, at a research building of the University of Freiburg, located in southwestern Germany, the adaptive shades unfurled themselves into a mostly closed configuration, as shown here. It was 17.5 °C outside, with a relative humidity of 37.4%. In weather that is colder and damper, a common combination in Freiburg, the shades curl. That allows more sunlight to come in through the window and warm the indoor environment. The designers—Tiffany Cheng, Yasaman Tahouni, and Ekin Sila Sahin, all at the University of Stuttgart, and their colleagues—were inspired by biological materials such as pine cones that passively change shape in response to moisture.

The team’s prototype shades are made of renewable cellulose. The structure consists of fiber-like strands that swell in a preferred direction when they absorb moisture, and that swelling makes the entire shade panel bend. Initial tests show that the shades’ curling depends predominantly on humidity and to a lesser extent on temperature. More work is necessary to determine how effective the shades can be in climates where hotter days are humid and colder ones are dry. Adaptive window shades won’t eliminate the need to heat and cool buildings, but they may help lower the energy requirements for building operations, which are responsible for 27% of global carbon dioxide emissions . (T. Cheng et al., Nat. Commun. 15, 10366, 2024 ; photo courtesy of Tiffany Cheng.)

This article was originally published online on 28 January 2025.