Abstract: A method of making a catheter balloon, and a balloon formed thereby, in which a polymeric tube is radially expanded in a mold having a wall with an outer surface and an inner surface defining a chamber, and having at least a section with one or more channels in the wall. The channels result in improved transfer of heat to the polymeric tube within the chamber of the mold during blow molding of the tube to form a balloon, so that the tube is heated more quickly and evenly. One aspect of the invention is directed to a balloon having sections with improved thin walls.