Carbon raised $260 million that should help it advance toward the ability to 3D print products made of multiple materials. Carbon already sells 3D printers used to make unusual the materials inside Riddell’s custom-size professional-league football helmets and Adidas running shoes. Now, a new $260 million funding round should help the Silicon Valley startup create even more unusual materials.  Also called additive manufacturing, 3D printing got an early foothold as a way to design prototypes. Since then, it’s also  crept into production lines for finished products. The unusual shapes of 3D-printed elements let companies build plastic components that are lighter than metal alternatives but couldn’t be made with conventional injection molding methods, for example. The result is a potentially dramatic change to what’s possible in manufacturing — more flexibility, more advanced designs, custom-tuned material properties and components that are built in one pass instead of assembled from a collection of parts. People on a Mars mission could build replacement parts as needed instead of carrying an inventory of everything. Oh, and yeah, people can 3D print ...