Most home metal-casters use traditional green-sand molding techniques to cast parts. Typically, a two-part molding flask is packed with specially-treated sand around a pattern, then the flask is carefully opened, the pattern removed, and the flask reassembled, being careful not to disturb the sand impressions, leaving a negative space in the exact shape of the original. In lost-foam casting, however, the pattern does not have to be removed before pouring in the molten metal; rather, the hot melt simply vaporizes the foam as it flows in, and replaces it. This process has a number of advantages to recommend it over the traditional technique. It does not require a two-part flask, and can be performed in a simple metal bucket. Nor does it require special sand, or special techniques for handling it. Dave Kush has a great overview on his site. Among other things, Dave uses the lost-foam process to cast homemade linear bearings for his CNC equipment.