Forget plastic, glass, ceramic, and metal. Sand could become the most important 3-D printing material out there.

Thanks to sand casting, which accounts for over 70% of metal casting, 3-D printing companies capable of printing with sand have a tremendous opportunity to benefit. In the video below, Fool.com contributor Steve Heller details the process of sand casting and how 3-D printing companies like 3D Systems (NYSE:DDD), Stratasys (NASDAQ:SSYS), and ExOne (NASDAQ:XONE) could all stand to benefit.