Lost form (full-mold casting) is a technique similar to investment casting, but instead of wax as the expendable material, polystyrene foam is used as the pattern. The foam pattern is coated with a refractory material. The pattern is encased in a one-piece sand mold. As the metal is poured, the foam vaporizes, and the metal takes its place. This can make complex shaped castings without any draft or flash. However, the pattern cost can be high due to the expendable nature of the pattern.