Duraline 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. Dura-Line Smooth Wall HDPE conduit can be used both as outer conduit or as innerduct. Flexible HDPE makes gradual bends without using special tools or equipment. It is co-extruded with SILICORE® ULF lining for longer cable pulls and higher speed jetting. Continuous lengths/long reels reduce cost from joins. Suitable for direct burial, direct bore, HDD, aerial, trench, tray and plow installation methods and for telecommunications, electrical, industrial, municipal and other underground applications.