A process used to create hard and brittle solid materials from a powder, reduce the porosity of metals, and increase the density of ceramic materials. It uses a very high pressure of around 1000 bar and temperature of over 1,000ºC depending on the materials. Ceramics and diamond-metal composites are made using this process in which the powder particles pack to form a very dense material. An inert gas such as argon is used to prevent oxidation of the materials.