Slabs are loaded into a high-pressure autoclave. The material is heated above its melting point and pressurised with pure nitrogen gas. Over a long period of time the nitrogen gas diffuses into the slabs. A rapid depressurisation destabilises the absorbed nitrogen, nucleating cells in the slab. The slabs are then cooled under pressure in the autoclave, locking the nitrogen in the un-expanded slabs, prior to them being unloaded. Operating temperatures reach up to 250ºC / 482ºF and pressures 675 bar / 10,000 psi.