Articulated riprap is usually fabricated so that the individual elements are keyed together, and then secured by connecting cables or strands run in two directions to hold the units together. Articulated riprap is usually placed on a filter bed, engineering fabric, or both. The riprap is so named because it is flexible and can move as a unit with the slope and still remain intact. There are several commercial sources of articulated riprap. Each should be evaluated for price, performance, and experience.