It’s the dead of January, and your living room is so cold that the chill seeps into your bones, and you can barely feel your fingertips. You might crank up the thermostat. But soon you could be cozying up in a self-heating sweater.
Engineers at Stanford University have figured out how to coat clothing in a meshwork of silver nanowire so that it not only insulates better than regular clothes but also generates its own heat. And cheap versions could hit store racks in three years, predicts Yi Cui, an associate professor of materials science and engineering at Stanford who led the project, described in Nano Letters last November.
Cui and his colleagues came up with the idea for the fabric when considering that nearly half of the world’s energy consumption goes toward heating buildings — which contributes to up to a third of global greenhouse gas emissions. To reduce energy waste and keep heat indoors, most engineers have tried to boost the insulating properties of building materials. But the Stanford team turned its focus to keeping people warm. Regular clothing can do this by trapping heat, but it allows much of that heat to dissipate back into the surrounding air.
Since silver can conduct electricity, a mini battery could deliver a small voltage to heat up the nanowires for extra warmth.
Why not use metal? The surface would reflect heat radiating from the body back onto the skin. But metal is hard, and people want clothing “to be soft and still breathe,” Cui says. The solution: soft, ultrathin nanowire. Cui decided on silver — cheaper than gold but more stable than copper, which forms a green crust when exposed to air. And since silver can conduct electricity, a mini battery could deliver a low-voltage current to heat up the material for extra warmth. To coat the fabric, Cui’s group immersed it in a solution that left behind a thin nanowire layer when dried, producing a fabric that still lets sweat escape and nanowires that don’t flake off in the wash.
Because nanowires are so thin, only a little silver is needed. Benjamin Wiley, an assistant professor of chemistry at Duke University, calculates that the coating would add just 10 bucks to the cost of a shirt at most. Meanwhile, Cui estimated that wearing the material would save around 1,000 kilowatt-hours per person a year — about the amount of electricity that the average U.S. home uses every month.
But would people wear a nanowire-coated sweater? Weaning them from their heating systems might take more than just warmer clothes. Although layers are an option, many would still rather turn up the heat, Wiley says. Lowering energy use “doesn’t just require a technology. It requires changing how people live their lives.”
Next up, Cui wants to continue improving the durability of the material. Also in the works: a self-cooling fabric that could make people rely less on their ACs. Soon enough, contending with global warming might be as effortless as throwing on your shirt in the morning.
Why you should care
Nanowire-coated clothing might not only keep us warmer — it might also be our next weapon against climate change.