Researchers are working on smart windows which would block the out heat when it's hot outside.

However, the current methods for making these windows use jelly-like materials called hydrogels that swell in the heat, which hurts performance.
Building on previous advances, the researchers hence made a version of the hydrogels, but in the form of microscopic soft beads suspended in a liquid. They sandwiched the solution between two pieces of glass and tested it using a model house. When they shined a lamp mimicking solar light on the smart window, it turned opaque and kept the inside of the house cool. The microgel, however, didn't swell as much as its predecessor.
The findings are reported in ACS' journal Industrial and Engineering Chemistry Research.
Source-ANI