Abstract: A tube or hollow body of a plastic material having memory characteristics is formed in a mold body having interior undulations or grooves. Pressure is applied to the interior of the plastic tube, while the tube is at a temperature above its softening point, to expand the tube into the configuration of the interior of the mold body. The pressure is maintained while the tube is cooled. After cooling, the tube is extracted axially from the mold body, and is reheated to cause the tube, by virtue of its memory characteristics, to return to the shape it had while in the mold, thereby eliminating the distortion and stretching occurring during removal from the mold. The mold body can be a tubular corrugated casing or stainless steel with a relatively thin wall, which cannot be taken apart. End assemblies are provided to hold and seal the tube ends while the tube is expanded in the mold body, by pressure applied through one of the end assemblies. The preferred plastic material is PTFE (TEFLON).