Nano Lett. http://doi.org/xq9 (2014)

Heating up buildings consumes nearly half of global energy and contributes significantly to the global energy crisis. To reduce indoor heating, most efforts have focused on installing better insulation in buildings, rather than managing heat loss from people. Yi Cui and colleagues at Stanford University have now shown that silver nanowire-coated cloths can reduce body heat loss and/or raise body temperatures when worn.

The researchers dipped a piece of cotton textile into a dispersion of silver nanowires, which created a porous and conducting network of nanowires on the cloth. Simulations and experiments showed that, due to the approximately 300-nm spacing between the nanowires, the coated cloth effectively reflected most of the radiation from the human body (which peaks at approximately 9 μm in wavelength), thereby allowing most of the heat to be trapped around the skin. Moreover, at this nanowire spacing, water vapour from perspiration can easily escape, making the material comfortable to wear. Further experiments showed that the silver nanowire coating offered 21% more thermal insulation than uncoated cloth. When a voltage was applied, the coated cloth could also actively warm up through Joule heating.

Cui and colleagues estimate that approximately 355 watts per person can be saved if silver-coated clothes are worn, suggesting that it could be a promising way to reduce the power demands of heating our homes.