Researchers at Stanford University in the US developed insulating paint in multiple colours that can keep buildings cooled in summer and warmer in winter, reducing energy use, costs and greenhouse emissions.

The heating and cooling of spaces accounts for about 13 per cent of global energy use, and about 11 per cent of greenhouse gas emissions.

Other low-emissivity paints usually have a metallic silver or grey colour, which limits their use aesthetically. The new paint works with two layers that are applied separately. The first one is an infrared reflective bottom layer using aluminium flakes. The second one is an ultra-thin, infrared transparent upper layer, made with inorganic nanoparticles that come in many colours. The infrared spectrum of sunlight causes 49 per cent of natural heating of the planet when it is absorbed by surfaces.

To keep the heat out, the paint can be applied to exterior walls and roofs. Most infrared light passes through the top layer and reflects off the bottom one, though the top colour layer also reflects some near-infrared light. Thus, the building does not absorb the heat and is not warmed. To keep the heat in, the paints is to be applied on interior walls, where the same process happens, trapping heat inside.

Up to about 80 percent of high mid-infrared light is reflected by the paints, doing most of the work of keeping heat inside during cold weather and outside during hot weather. The insulating paint was tested in various colours, including white, blue, red and dark grey. The new paint reduced the energy used for heating by about 36 percent in experiments using artificial, cold environments. They reduced the energy needed for cooling by almost 21 percent in artificial warm conditions.

The paint is not only interesting for use on buildings, but also for example trucks or trains that have refrigerated transportation.

Photo: Yucan Peng