This paper investigates a new constitutive model of the competitive swimwear considering stress-softening. The purpose of this study is establishment of an engineering technique using numerical analysis to make the design for swimwear more effective. Effective design considering mechanical characteristics would be an advantage in swimming competitions. The fabrics for competitive swimwear show nonlinear elasticity regarded as hyperelasticity and they have an anisotropic characteristic which is dependent on the directions of warp and weft yarn. In order to reproduce these properties numerically, hyperelastic model considering anisotropy was produced. In addition, the fabrics present a loss of stiffness after first loading of cycle loading test. This phenomenon depended on the maximum deformation previously reached in the history of the material. To account for the stress-softening property, a stress-softening model using stiffness ratio of warp or weft was proposed. Then, cyclic loading tests were conducted and the applicability of the model was verified.
