A catheter balloon and method involves extruded tubing with multiple layers of different durometer values, selected such that the blow up ratio (BUR) at the balloon's inner surface is increased. In one method a two stage blow mold process uses a small radius initial stage where radial growth is limited, followed by a second stage to a final dimension. A single stage blow mold process is also disclosed where the materials and processing are selected to approach the elongation to failure limit of the material. The single stage approach is preferably followed by a modified post-expansion heat set treatment to promote greater axial strength, leading to a preferred failure mode in the axial rather than radial direction.