Expanded polystyrene articles are manufactured from polystyrene granules that incorporate a blowing agent – a substance which, when heated, gives off a gas. This may be a volatile liquid (such as pentane) or a carbonate. These granules are then steam-heated and the gas from the blowing agent expands to produce a foam plastic. This gas is eventually exchanged with air. Thus the gas in the solid foam is largely air.

The expanded polystyrene does not actually dissolve in the propanone; it merely softens as it absorbs the propanone and allows the air to escape, thereby collapsing the foam. An interesting example of a gas formed not by a chemical process, but by a physical process. The resulting colloidal gel consists of propanone molecules dispersed in a network formed by a tangle of large polystyrene molecules – a similar structure to ordinary jelly in which water molecules are dispersed in a network of protein molecules.

Sustainable Cities and Communities: SDG 11 advocates for sustainable urban development, which includes creating resilient and resource-efficient cities. Styrofoam insulation in house walls can help reduce energy consumption and greenhouse gas emissions, promoting sustainability in the construction sector. In the magic trick using styrofoam we can explore its use in construction and we can also take the opportunity to discuss whether this is a sustainable material and possibly think about alternatives.