The sun has risen, and a brand new building on the University of Washington’s campus in Seattle is about to melt.

It is no design flaw: encapsulated within the walls and ceiling panels is a gel that solidifies at night and melts with the warmth of the day. Known as a phase change material (PCM), the gel will help reduce the amount of energy needed to cool office space in the building – scheduled to house the molecular engineering department when completed this month – by a whopping 98 per cent.

PCMs don’t have to be as high-tech as this, of course. We have been using ice, a phase change material that melts at 0 °C, to keep things cool for thousands of years. But advances in materials science and rising energy costs are now driving the development of PCMs that work at different temperatures to help people and goods stay cool or warm, or to store energy.

PCMs are attractive energy-savers because of their ability to absorb or release massive amounts of energy while maintaining a near-constant temperature. “To melt ice takes the same amount of energy as would be required to warm an equal volume of water by 82 °C,” says Jan Kosny of the Fraunhofer Center for Sustainable Energy Systems in Cambridge, Massachusetts, who began to explore the potential of PCMs three decades ago by looking at beeswax as a way to store heat from the sun. The reason PCMs are so useful is because energy is needed to break the molecular bonds between atoms when a substance melts, and is released when bonds are formed as it solidifies.

The “bioPCM” gel in the university building, derived from vegetable oils, will be “charged” each night when windows automatically open to flush the building with cold outdoor air. The solid gel then absorbs heat as it melts the next day. The idea is the same as using thick concrete or adobe walls, which reduce indoor temperature fluctuations, but only a fraction of the material is required. “Our bioPCM is 1.25 centimetres thick yet it acts like the thermal mass of 25 centimetres of concrete,” says Peter Horwath, founder of Phase Change Energy Solutions, based in Asheboro, North Carolina. » Read more: Buildings and clothes could melt to save energy