Lost foam molds, also known as expendable foam molds, are a type of casting mold that utilizes a lightweight, porous foam material as the pattern. This foam pattern, once shaped into the desired casting geometry, is coated with a refractory material and then placed within a larger mold cavity. When the molten metal is poured into the cavity, the foam pattern burns away, or "loses," leaving an empty space in the mold that corresponds to the desired casting shape.

The lost foam casting process offers several advantages, including the ability to create complex geometries that would be difficult or impossible to achieve with traditional casting methods. It also allows for near-net-shape casting, reducing the amount of post-processing required. Additionally, the foam patterns are relatively inexpensive and easy to produce, making lost foam casting an economically viable option for many applications.

However, lost foam casting also has some challenges, including the need for precise control of the foam pattern's decomposition rate to prevent defects in the casting. Additionally, the process can be sensitive to changes in mold temperature and metal pouring conditions, which can affect the quality of the final casting. Despite these challenges, lost foam casting has become a widely used technique in a variety of industries, including automotive, aerospace, and medical device manufacturing.