Suitably named Water-Filled Glass (WFG), the start-up has developed special panes containing a thin layer of water which is warmed by sunlight. The heated water is subsequently pumped through the building to warm cold areas.

Matyas Gutai, co-founder of WFG, told Dezeen: “We know that putting water in the window sounds like an outright mad idea.

“But we believe this is important because when you think about the energy of buildings and cutting carbon emissions, there’s still great potential and opportunity to think about glazing.

“Glass is responsible for a great part of heating and cooling energy consumption, and it’s a ubiquitous material, it’s on almost every building.”