A solid, made by a parallel shift of a polygon is called prism.
In the FEM, prisms with triangular footprints are commonly used.
Its advantage is an unstructured mesh in two directions, and, at the same time, one structured main direction.
Based on the surface mesh out of triangular -elements prism- elements are extruded into the part.
Different layers of the so built prism-elements are possible. In combination with tetraeder-elements (in the remaining part), a blm mesh is built with a high accuracy and less elements. Therefore, the calculation time can be reduced.
The special form of the triangular footprint based prisms allows, in the runner system for injection molding simulation, an orientation of the fibers in flow direction inside the runner without a secondary preferred direction.