The polymer is called Poly(N-isopropylacrylamide, or PNIPAM.
It is made into a mat and covered by a membrane that allows water to soak through it. When it rains, the mat acts like a sponge, soaking up water. But put it in direct sunlight at a temperature of 32 degrees Centigrade (89.6 degrees Fahrenheit), and it shrinks while taking on hydrophobic properties, squeezing the water out, essentially sweating.
The mats were tested on small, model houses - the size of those used on model train sets - and was able to cool more efficiently than conventional polymers. It also insulated the houses so that they heated up more slowly.
The next step is to test the mats in the cold - it is not clear yet how they might react to being frozen. Even so, if it can be made on a large scale such mats would be useful for people who live in rainy, tropical areas where there is a lot of rain and heat, and where air conditioning is expensive to install.
The research was published online in the journal Advanced Materials.
Credit: Aline Rotzetter / Advanced Materials