convoluted tubing of thermoplastic resin is made by extruding the resin as a molten tubular extrudate , feeding said extrudate into the interior of a rotating tubular member which has a helical thread in the interior of said member , the spiral thread having a deformation zone receiving the extrudate and a cooling zone downstream from the deformation zone . a vacuum can be used to force the extrudate against the spiral thread in the deformation zone to spirally convolute the extrudate . the rotation of the tubular member causes the resultant convoluted tubing to engage the spiral thread in the cooling zone for conveyance through such zone . apparatus comprising the rotating tubular member with the interior thread for forming the convoluted tubing is provided .