Windows might one day become more energy efficient with help from a self-regulating thermal coating, according to a report in Nature (DOI: 10.1038/nature11223). Joanna Aizenberg of Harvard University, Anna C. Balazs of the University of Pittsburgh, and colleagues developed polymer-based materials that maintain their internal temperature within a 1.7 °C range regardless of surrounding conditions. Called SMARTS, for self-regulated mechanochemical adaptively reconfigurable tunable system, the coatings are composed of catalyst-tipped microposts embedded in a temperature-responsive poly(N-isopropylacrylamide) hydrogel. A thin liquid layer containing chemical reagents rests atop the gel. Like hairs on a person’s arm, the tiny posts stand up at low temperature as the hydrogel absorbs water and swells. The catalyst on the post tips then reacts exothermally with compounds in the reagent layer, causing the gel to heat and contract. When that happens, the posts flop over, moving out of reach of the reagent layer. Thereafter, the cycle repeats as the chemical reaction switches on and off in a feedback loop. Besides being useful to control weather-responsive building materials, the patented SMARTS might also be incorporated into biochemical sensors, robotics, and medical implants, Aizenberg says.