Dura-Line Smooth Wall HDPE Innerduct Conduit. All Dura-Line's smooth wall conduit meets or exceeds one or more of the following standards: ASTM F-2160, ASTM D-3035, ASTM D-2239, ASTM D-3485, NEMA TC-7, UL 651, UL 1990, Bellcore GR-356. Flexible HDPE allows gradual bends without special tools. Available in multiple sizes (1/2" to 6"), SDR ratings (including SDR 13.5), and colors (including orange). Suitable for direct burial, HDD, plow, aerial, tray, and other installations.