Abstract: An expandable section plastic tube having utility, for example, in inflatable balloon section catheters, and a method of making the same. The tube formed of thermoplastic material is inserted in a wall defining member, such as a mold, having an enlarged section surrounding a portion of the tube. The tube portion is then heated to a thermal plastic temperature and is expanded into the enlarged section by a sudden application of pressure resulting in a thinning of the tube wall in the expanded area. Thereafter, the tube is cooled and removed from the mold. In the making of a catheter, one section of the tube to one side of the expanded area is inverted and drawn into the section of the tube on the other side of the expanded area whereby the expanded area forms a balloon end at one end of the telescoped tube sections.