The physical properties of polyurethane elastomers depend strongly on the polymer structures, which have many variables, such as the composition of the polyester, chain extender and isocyanate. By increasing the molecular weight of diols in polyester and the content of the chain extender, the modulus and tensile strength were increased, whereas the elongation was decreased. By increasing the ratio of TDI/MDI, the molecular weight of chain extender and of the polyester, the polyurethane showed a low tensile strength and a high elongation. In order to have elastomer properties, polyurethane had to contain urethane groups more than a definite concentration in the polymer chain.