Wettability basics

Will it soak in or be repelled?

10 minutes


  • Carefully review the general safety advice on the back of the box cover before starting the experiment.
  • Perform the experiment on the safety tray and use protective gloves to avoid staining your hands.
  • Never eat or drink any of the substances provided. Do not use for culinary purposes.


  • Dispose of solid waste together with household garbage.
  • Pour liquids down the sink. Wash with an excess of water.

Scientific description

Everything consists of tiny invisible particles—molecules. Within a single material, the attraction and repulsion between its molecules determine its external characteristics: whether it is liquid or solid, elastic or rigid, and so on.

The molecules of two different materials  interact with each other when they come into contact. On any flat surface, a water droplet  adopts a round shape , the width of which depends on the surface material. The stronger the attraction  between the molecules of water  and the material , the wider the drop spreads . If the material has a porous structure and consists of molecules  that attract  water molecules , the drop of water will seep into the material and fill its pores.

A material with molecules  that are weakly attracted to water molecules  is said to be hydrophobic (from the Greek "afraid of water"). On a material like this, a drop of water will tend to adopt a spherical shape  due to its weak connection with the surface. A material composed of molecules  that strongly attract water molecules  is said to be hydrophilic (meaning "water-loving"). On such a material, a drop will spread over a large area , trying to increase its contact with the surface as much as possible.