An expandable medical balloon, the expandable medical balloon comprising: a first balloon wall, the first balloon wall comprising a first balloon layer of polyethylene terephthalate having a first intrinsic viscosity, the first balloon layer is outer to a second balloon layer of polyethylene terephthalate, the second balloon layer of polyethylene terephthalate having a second intrinsic viscosity, the second balloon layer is an inner layer, wherein the intrinsic viscosity of the first balloon layer is higher than the intrinsic viscosity of the second balloon layer by 0.05 dl/g or more, and wherein the inner diameter hoop ratio of the first balloon outer layer is 6.0 or less as determined by the following formula: Mold ID Tube ID wherein the Tube ID is the inner diameter of the first balloon outer layer and Mold ID is the inner diameter of the mold in which the expandable medical balloon is formed; wherein the expandable medical balloon has a calculated burst strength of 50,000 psi (344,737,865 Pa) or greater as calculated by the following formula: Strength = P × D / 2 t where P = internal pressure when the balloon bursts (psi) (Pa); D is the exterior diameter (inches) (mm) of the balloon when an inflation pressure of 118 psi (813,581 Pa) is applied; and t is the wall thickness of the portion of the balloon with the larger exterior diameter (inches) (mm). a first balloon wall, the first balloon wall comprising a first balloon layer of polyethylene terephthalate having a first intrinsic viscosity, the first balloon layer is outer to a second balloon layer of polyethylene terephthalate, the second balloon layer of polyethylene terephthalate having a second intrinsic viscosity, the second balloon layer is an inner layer, wherein the intrinsic viscosity of the first balloon layer is higher than the intrinsic viscosity of the second balloon layer by 0.05 dl/g or more, and wherein the inner diameter hoop ratio of the first balloon outer layer is 6.0 or less as determined by the following formula: Mold ID Tube ID wherein the Tube ID is the inner diameter of the first balloon outer layer and Mold ID is the inner diameter of the mold in which the expandable medical balloon is formed; wherein the expandable medical balloon has a calculated burst strength of 50,000 psi (344,737,865 Pa) or greater as calculated by the following formula: Strength = P × D / 2 t where P = internal pressure when the balloon bursts (psi) (Pa); D is the exterior diameter (inches) (mm) of the balloon when an inflation pressure of 118 psi (813,581 Pa) is applied; and t is the wall thickness of the portion of the balloon with the larger exterior diameter (inches) (mm). wherein the Tube ID is the inner diameter of the first balloon outer layer and Mold ID is the inner diameter of the mold in which the expandable medical balloon is formed; wherein the expandable medical balloon has a calculated burst strength of 50,000 psi (344,737,865 Pa) or greater as calculated by the following formula: Strength = P × D / 2 t where P = internal pressure when the balloon bursts (psi) (Pa); D is the exterior diameter (inches) (mm) of the balloon when an inflation pressure of 118 psi (813,581 Pa) is applied; and t is the wall thickness of the portion of the balloon with the larger exterior diameter (inches) (mm). where P = internal pressure when the balloon bursts (psi) (Pa); D is the exterior diameter (inches) (mm) of the balloon when an inflation pressure of 118 psi (813,581 Pa) is applied; and t is the wall thickness of the portion of the balloon with the larger exterior diameter (inches) (mm).