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. Smoothwall conduit is available in multiple SDR wall thicknesses, colors (including orange), optional SILICORE 4 ULF lining, and continuous long-reel lengths for reduced joins. Installation methods include direct burial, direct bore, HDD (horizontal directional drilling), aerial, trench, tray, and plow.