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. Co-extruded with SILICORE® ULF lining for longer cable pulls and higher speed jetting. Continuous lengths/long reels reduce cost from joins.