Smooth Out / Ribbed In HDPE conduit from Dura-Line (6" SDR 13.5). This product features a smooth outer wall with internal longitudinal ribs to reduce friction, offering flexibility for gradual bends and installation across aerial, direct-buried, trench, plow, and directional-bore applications. Manufactured from HDPE for low-temperature performance and long-term protection of contained cables; available in multiple colors and optional features such as UV protection, pre-installed tape or cable, and color stripes.