Production is available in various stiffness classes from SN 4 to SN 16. The low friction coefficient of the inner surface (k = 0. 013 mm) allows for high-flow fluid transfer. Developed by Esen Plastik, Spiral Wound Corrugated Pipes are manufactured from high-density polyethylene (HDPE) using advanced extrusion and spiral winding technology. The outer surface of the pipes is produced in a spiral form to enhance ring stiffness, while the inner surface is designed to be. Spiral HDPE Pipe manufactures a spirally wound structured wall pipe from PE-HD, known as SPIRAL Structured Wall HDPE Pipe. The SPIRALStructured Wall HDPE Pipesystem is economical and competitive, as the structured wall concept. International Dielectric Products, Inc.