2. Manufacturing techniques

Since the 1950s, numerous processes have been developed to manufacture metal foams. Several classifications can be used to group them together. For example, the physical state of the metal during shaping (liquid, solid, gaseous or ionic) could be a classification criterion. In this section, we have preferred to group these processes according to the physical principles they call upon, even if their practical implementation may differ. This allows us to present the said principles for each of these groups of processes, before going on to describe the various existing implementations.