The Xtra Flex forming system is available for forming concrete 12 inches high. Standard 10-foot lengths of the four-inch, six-inch and the new 12-inch are made from High Density Polyethylene (HDPE) to form tight radii from 36 inches to as small as nine inches. The Xtra Flex system offers several advantages: Long life: no need to constantly replace materials that disintegrate with exposure to harsh job site conditions; Quick grade elevation adjustment; Positive end connection; Easy to set and strip: bolt-on steel stake pockets with easy grip locking knob.