Just as mammals can reduce their body temperature by sweating, so a coating of heat-sensitive hydrogel could 'sweat' to cool buildings.

Credit: WILEY-VCH VERLAG GMBH & CO. KGAA, WEINHEIM

Wendelin Stark and his colleagues at the Swiss Federal Institute of Technology in Zurich produced a 3-millimetre-thick layer of thermoresponsive hydrogel. When heated to roughly 32 °C, the gel undergoes a phase transition from a wet state to a dry state, and releases water. With this water could go much of a building's heat.

Miniature model houses (pictured) with roofs coated with the substance were up to 20 °C cooler than uncoated models when exposed to simulated tropical midday Sun. The authors estimate that this translates into annual savings of 220 kilowatt-hours of energy for a detached house. A brief 'rain' recharged the hydrogel with water.

Adv. Mater. http://dx.doi.org/10.1002/adma.201202574 (2012)