an expander member for a balloon catheter to be used in stent delivery applications comprises a double - walled tubular member that is adapted for attachment to a distal end portion of an elongated , flexible , tubular catheter body . the outer wall is preferably a polyamide , such as nylon - 12 , and the inner wall is pet . by properly controlling the percentage of the polyamide relative to the pet content , the distension characteristics of the resulting expander member can be tailored to fall in a range less than 15 percent . the outer nylon - 12 layer provides the expander member with high abrasion resistance . by appropriately temperature annealing the expander member , any tendency toward winging upon deflation thereof is reduced .