1. The bottle – before use
Before use, the contents of the bottle are in three different parts: the emulsion is at the bottom, above this is the liquid part of the propellant, and the gaseous part is at the top.
2. Shake first ...
When you shake the bottle, the liquid part of the propellant mixes with the emulsion.
3. ... then hold upright!
When you press the spray head, the gaseous part of the propellant pushes the mixture through the ascending tube and out of the bottle. Once it leaves the bottle, the propellant in the emulsion expands abruptly and becomes gaseous, creating the foam cream.
If the can is held with the spray head pointing downwards, the open end of the riser tube projects upwards into the gaseous part of the propellant. This way, only propellant can escape when the valve is opened.