A vast range of products are packaged in aerosol containers. The product is dissolved or suspended in a liquid solvent concentrate. A liquefied gas usually acts as the propellant; the propellant in its liquid state is very often part of the solvent system.

In a typical aerosol some of the propellant exists as a gas under pressure above the liquid mixture. This gas pushes down on the liquid, forcing the liquid up through the dip tube and through the valve when opened. This liquid is a mixture of product concentrate with liquefied gas. As this mixture is used up, gas evaporates from the liquid inside the container to give a constant pressure, thus giving a consistent performance through the life of the pack.

When you press the button on an aerosol container, the valve opens and the product mixture is pushed out because the pressure inside the can is higher than the pressure outside. 

When the mixture leaves the can, the liquid propellant becomes a gas and helps to break the spray into droplets, so giving a finer spray - the aerosol. In foam or mousse, the liquefied gas forms bubbles to make the product 'grow' once it is outside the container. The liquid propellant is also a quick drying solvent, in paint for example. The actual amount of propellant found in an aerosol container varies depending on the product; a higher percentage for fine sprays, low for foam or mousse.

To find out more about aerosols, visit the Schools’ Physics Resources section of our website and link into the school science website at www.schoolscienceco.uk. Teachers can also source free of charge classroom posters about aerosols from our Guides & Publications section in About BAMA.