The structure of a hailstone reflects its growth history. It can be translated through experiments in icing-wind tunnels. Knowing the shape allows us to deal with free fall, and, based on it, with heat and mass transfer - which controls freezing. The various facilities used in his venture will be discussed, together with the ‘New Hailstone Physics’. Thereby a big factor is played by ‘Spongy Ice’, an ice lattice that is filled with water. It explains the explosive growth of hailstones.