Lost foam casting is a sand casting process that uses an expandable polystyrene (EPS) pattern that embodies the positive shape of the part to be cast. Lost foam casting is especially suitable for fairly complex castings with many internal passages. This article discusses the advantages and the process technique of lost foam casting. It describes the pattern molding for the lost foam process that is grouped into four major functions: filling, fusion, cooling (stabilization), and ejection. The article provides information on the application of the pattern coating. It concludes with a review of the quality of the lost foam casting in terms of dimensional tolerances, fold defects, and porosity.