a process for making porous flexible pipes from two feed streams containing a thermoplastic material and a thermoset material , in which the feed streams are delivered to a die head extruder in a substantially compaction - free and segregation - free manner to insure that the feed composition in the extruder is substantially the same as the initial feed composition . the process can be automated so that an operator can manufacture porous flexible pipes of desired porosity and other rheological and mechanical characteristics by simply entering a command which will simultaneously adjust the process parameters such as the temperature and / or pressure inside the extruder , and the post - extrusion tension to meet the special need .