Hydrogel is a moisture-absorbing polymer capable of absorbing up to 400 times its own volume in water, then as the water evaporates, it cools down the area around it.
The hydrogels then refill themselves when humidity is high on the outside. With the help of this “passive cooling” concept, these walls can reduce room temperature in up to 5°C without the use of air conditioning and reduce energy consumption by 28 percent.
via Students create hydroceramic wall that could replace the use of air conditioners.