In bad news for blinds and curtain makers, scientists have created a window glass that can block heat and sunlight at the flick of a switch.
The "smart glass" has a thin covering of nano-crystals of "indium tin oxide embedded in a glassy matrix of niobium oxide".
When an electric an electric current the glass blocks out heat and light, the amount of which can be varied depending on voltage.
Delia Milliron, a chemist at the Lawrence Berkeley National Laboratory where the technology was developed, said: "In the US, we spend about a quarter of our total energy on lighting, heating and cooling our buildings.
"When used as a window coating, our new material can have a major impact on building energy efficiency."
Other technologies like Sonte Film allowed for light to be allowed in but did not keep out heat.
The indium tin oxide in the glass blocks out heat and causes the niobium oxide to absorb five times as much light as it would on its own.
It cannot currently block out 100 per cent of heat but the researchers are working on improving this.