When making bottles, air is blown into the molten glass through a tube

When making bottles, air is blown into the molten glass through a tube, and the shapeless mass takes the desired shape. What physical phenomenon is used here?

Here a physical phenomenon takes place, which is due to the fact that the gas fills the entire available volume. Here we can talk about the laws of static thermodynamics, for example, about the Gay-Lusac or Boyle-Mariotte law. You can also talk about atomic physics, since we are talking about the properties of atoms to attract and keep the relationship in matter (in a gas these bonds are minimal, that is why it fills the entire volume).