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Buildings of the future may have mirrors that reflect sunlight into space to keep them cool.

Developers of the new technology hope the concept could lead to a cheaper and more sustainable form of air conditioning.

Their incredibly thin material offloads heat from the sun into space in the form of infrared radiation, and could keep buildings 5°C (9°F) cooler than the surrounding air during the day.

Scientists at Stanford University in California have created an ultra-reflective mirror. The incredibly thin material reflects infrared light from buildings (illustration shown), and it could be placed on top of buildings to keep them cool in hot weather by reflecting infrared radiation into space

The technology was developed by scientists at Stanford University in California.

It consists of a multi-layered material that is just 1.8 millionths of a metre thick, thinner than the thinnest aluminium foil.

This material is made of seven layers of silicon dioxide and hafnium oxide on top of a layer of silver.

The internal structure of the material radiates incoming infrared rays back into space.

Invisible light in the form of infrared radiation is one of the ways that all objects and living things throw off heat.

For example, when standing in front of an oven without touching it, the heat felt is infrared light.

Sunshine, in a similar way, radiates heat to Earth and can significantly warm buildings in the hottest parts of the world unless they have air conditioning.

This cheaper method would prevent electricity needing to be used for air conditioning, and would instead just constantly keep buildings cool.

About 15 per cent of energy used in buildings in the US is apparently spent powering air conditioning systems.

The material would need to be installed on the roof of a building, where it would reflect heat straight back up into space.

The new material reflects 97% of sunlight, making the building 5°C (9°F) cooler than the surrounding air. They say it is a cheaper solution to air conditioning (stock image shown) as the planet warms

As it is highly reflective, placing it on the side of buildings would probably not be an option, as it would radiate heat onto the ground and potentially heat up populated areas such as cities.

But its potential for use on the top of buildings is obvious, and the team also think it could be used as a spray-on material to make objects more able to withstand the elements.

The researchers said that as the planet gets warmer, such cooling technologies that don't require power might become more commonplace.

'Across the developing world, photonic radiative cooling makes off-grid cooling a possibility in rural regions, in addition to meeting skyrocketing demand for air conditioning in urban areas,' said lead author Dr Aaswath Raman.

Right now the Stanford team's prototype is the size of a personal pizza, but cooling buildings will require larger panels.

The researchers say there exist large-area fabrication facilities that can make their panels at the scales needed, which will be needed before the prototype can be developed further.

More broadly, the team sees this project as a first step toward using the cold of space as a resource. In the same way that sunlight provides a renewable source of solar energy, the cold universe supplies a nearly unlimited expanse to dump heat.

'Every object that produces heat has to dump that heat into a heat sink,' Professor Fan said.

'What we've done is to create a way that should allow us to use the coldness of the universe as a heat sink during the day.'