Bentonite as a molding material binder consists of at least 75% of the three-layer material montmorillonite. The layers are created from the combination of an octahedron layer and two tetrahedron layers. Montmorillonite has a very high value in relation to three-layer clay minerals. The water molecules can be stored within the layer packages. The electroneutrality is disturbed by the introduction of charged ions into the octahedral coordination. The charge differences are eliminated by intercalating the ions between individual layers. The ion exchange ultimately leads to a considerable effect during activation and is essential for the foundry as an additive (auxiliary material).