The Densified Flakes are used as raw material for the Expanded Granules (lower density aggregates) production. CETMA developed a foaming/extrusion processes in laboratory and pilot scale. Within the NUMIX project, the industrial process has been definitively defined.

The density reduction is obtained through an extruder fed by the Densified Flakes and the gypsum powder used as blowing agent. At the exit of the extruder, thermodynamic processes lead to bubbles formation in the plastic mixture. For a good mixing of the blowing agent with the plastic and for a higher level of homogeneity of the granules a double screw extruder needs to be used. A filtering system provides to keep the bigger impurities which could obstruct the die. In order to let to the impurities and the higher melting point plastics to pass through the passage sections in the extruder, 3 mm filter mesh and die with 6 mm holes are recommended. An in-line cutter with a water ring die provides for the granulation of the extruded material, leading to the production of granules with regular shape.
Proper extrusion parameters (cylinder temperatures, die temperature, rotating speed) have to be used according to the double-screw extruder dimension and geometry.