As its name implies, expendable mold casting makes use of expendable molds for the casting process. This does not imply the use of inexpensive materials, however; the process refers more to molds that have to be broken to remove the materials cast rather than 'throwaway,' single-use molds.
Among the most common (and oldest) examples of the expendable mold technique is sand casting. Sand casting makes use of a "molding box" - actually a container filled with sand (usually 'green' sand) in which the patterns of the piece to be cast are set.
Expendable casting uses a variety of materials for the mold - plaster, concrete, resins, even wax (in the so-called 'lost-wax' or investment casting technique). Recently, polystyrene foam has been used in expendable casting for complicated and complex parts such as automobile engines and the like.
