Researchers at MIT developed self-cooling fabrics made from polyethylene, a material commonly used in plastic bags.

A plastic bag for a shirt hardly sounds like a cool option (both literally and figuratively). Polyethylene (PE) is thin and lightweight, and it lets heat pass through rather than trapping it. Therefore, it could keep you cooler than most fabrics. On the other hand, the material also locks in water and sweat, as it is unable to draw away and evaporating moisture, a large portion of how we cool down.

So, in order to make polyethylene a viable option, the MIT engineers spun polyethylene into fibres and yarns designed to wick moisture away. They started with polyethylene in powder form and used standard textile manufacturing equipment to melt and extrude thin fibres. The extrusion slightly oxidised the material, changing the fibre’s surface energy so that the polyethylene became weakly hydrophobic and able to attract water molecules to its surface.

The fibres were then bunched together to make weavable yarn. Within the strand, the spaces between the fibres formed capillaries through which water molecules could be passively be absorbed.

The researchers then wove the yarns into silky, lightweight fabrics that absorb and evaporate water more quickly than common textiles like cotton, nylon and polyester.

In addition to making the fabric, the researchers also calculated the ecological footprint that polyethylene would have if it were used as a textile. Perhaps counterintuitively, they estimated that the material actually may have a smaller environmental impact over their life cycle than cotton and nylon textiles. To the polyethylene fabric nothing sticks, which means it can to be washed less and cooler than other fabrics.

The researchers hope that fabrics made from polyethylene could provide an incentive to recycle plastic bags and other polyethylene products into wearable textiles, adding to the material’s sustainability.

Image: Felice Frankel, Christine Daniloff, MIT