Last updated February 23, 2018 at 3:53 pm
Every office in the world knows the problem – some people feeling cold while others sit around in short sleeves. There doesn’t seem to be a single temperature which keeps everyone comfortable. Enter a new fabric from California which might solve everyone’s complaints, and make reversible clothes the new fashion. This fabric has a neat party trick – wear it one way and it keeps you warm, but flip it inside out and it will keep you cool.
“Why do you need to cool and heat the whole building? Why don’t you cool and heat individual people?” asked researcher Yi Cui from Stanford University.
Our bodies have many ways of controlling our temperature. When it’s cold, the hairs in our skin stand out to trap warm air, and we shiver to produce more radiant heat in our muscles. When we’re hot, we release heat as infrared radiation from our skin, and if we’re still warm we start to sweat.
Fabrics able to heat or cool by taking advantage of the infrared radiation released from our bodies have been developed previously. However, seeing it as a challenge, Cui and his team decided to see if they could make a single fabric have both heating and cooling abilities.
The researchers started off with a polyethylene material they had previously developed. Similar to kitchen plastic wrap, this polyethylene is only 45 microns thick, but is made porous with nanometre sized holes. These holes allows body heat to pass through, keeping skin around 2° Celsius cooler, while also making the layer opaque so you can’t see through it.
The researchers then stacked two layers of material with different abilities to release heat energy. On one side, a carbon layer which strongly absorbs heat and re-releases warming infrared radiation. On the other, a copper layer which only weakly absorbs and radiates infrared radiation. Effectively, the infrared radiation is blocked from being released to whichever side the copper is facing.
To create the super-fabric, the researchers sandwiched the additional layers between different thicknesses of their polyethylene. Worn with a thin polyethylene layer facing inwards with the copper, and the carbon layer facing outwards, the garment cools by the carbon absorbing body heat and then radiating it outwards. Flip it around and the thick polyethylene layer is facing inwards with the carbon, which absorbs and reradiates body heat back towards the skin. The sandwich is so effective it can create a 6.5° Celsius difference in temperature depending on which way around it is worn.
Heating and cooling accounts for around 40% of energy use in the United States, making the development of personal climate-controlling clothing a creative and potential powerful way to reduce costs and carbon emissions. The multi-layer fabric is expected to be a relatively low cost solution, with the thin layers of each material being commonly available and affordable to manufacture.
Unfortunately however, we’re not likely to see the white-colored fabric on shelves in the near future, as the researchers are still trying to work out how to make it into a material which can be woven like a traditional fabric. “Ideally, when we get to the stuff you want to wear on skin, we’ll need to make it into a fiber woven structure,” said Cui. Woven textiles are stronger, more elastic, more comfortable, and look much more like typical clothing.
But most importantly of all: They have already started testing to make sure their fabric will be machine washable.
Fabric structure and emission comparison images from Hsu et al, Science Advances
Fabric image courtesy of Yi Cui Group