Corrugated PE rigid drainage pipes (also known as "rigid drainage pipes," "seepage pipes," "collecting water conduits," "blind gutters," etc.) are made primarily from high-density polyethylene (HDPE). They are formed by passing the material through a high-temperature extruder, which causes it to curve and oscillate, followed by cooling to create a pipe with one sealed side (commonly referred to as the impermeable layer) and the other side with uniformly dense small holes (commonly referred to as the permeable layer).