A tubular parison for forming a medical device balloon. The parison is formed of a polymeric material, for instance a thermoplastic elastomer. The parison has an elongation at break which is not more than 80% of the elongation of the bulk polymeric material. The elongation of the parison is controlled by altering extrusion conditions. Balloons prepared from the parisons provide higher wall strength and/or higher inflation durability than balloons prepared from conventional parisons of the same material.