Pore classes are a system for classifying pores in a material. They play a role above all in quality control in connection with primary forming manufacturing processes. Primary forming refers to a group of manufacturing processes in which a solid body with a geometrically predefined shape is produced from a formless material. Alongside electroforming and powder metallurgy, foundry technology is one of the most important urforming processes in manufacturing. Pores are small bubbles in the material, which can also occur in metal when casting technology is used. If an object has pores, it is porous; porosity refers to the presence or degree of pores in an object. In order to produce and process high quality porous materials, the effects of porosity in a workpiece must be accurately estimated. Pore classes, which are used to make such estimations possible via the surface characteristics of the porosity, help in this process. Based on the pore size, a general distinction is made between microporous and macroporous surfaces.