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 651/651A, UL 1990, Bellcore GR-356. Flexible HDPE conduit available in smooth inner/outer wall construction; co-extruded SILICORE® ULF lining option for reduced friction; available in multiple SDR/SCH wall types including SDR 11 for 3" size; packaging options include 40 ft sticks (per manufacturer technical documents).