• Here's what every other version of this experiment gets wrong: shaving cream is not a cloud, and this is not how rain forms.

Real clouds are not sponges. They don't hold liquid water and release it when they get too full. 

• A cloud is a suspension of microscopic water droplets — or ice crystals — floating in air.

So what IS this experiment showing? Percolation.

• Shaving cream is an aerosol foam: a porous matrix of tiny soap-coated air bubbles, packed together with small interconnected channels running between them. It's not solid — it's riddled with tiny gaps. 

• Food colouring is water-based and denser than the foam. When you place it on the surface, gravity begins pulling it downward through those tiny channels, squeezing between the bubbles, moving through the foam the way water moves through soil.

When the food colouring reaches the boundary between the foam and the water, it breaks through and streams downward — producing the colour trails that look so dramatic. The colour is heavier than the water it enters, so it sinks and diffuses as it falls.