Ballast is used to create a variety of rock materials for your layout or diorama. Available in various colors and fine medium course or blended grades you can be sure to find a ballast to meet your needs. Ballast track create roads driveways parks and landscaping or model natural rock. Great for mines or rock piles too. 21.6 cu. in. (353 cu. cm) bag. Please reference the Woodland Scenics ballast scale reference chart to help decide what type of ballast to use.