As a leader in human robotics, the UMass Human-Robot Systems Lab (HRSL) aims to develop a method to reduce energy expenditure during running. Previous approaches using rigid exoskeletons have successfully reduced energy expenditure during walking and jogging, with limited effectiveness at higher running speeds. To explore energy reduction at competitive running paces, HRSL is investigating the use of non-linear elastic materials. Effective implementation of this requires an unpowered exosuit capable of securely anchoring the elastic material between the torso and thighs. Our team was tasked with designing and fabricating the exosuit to facilitate efficient force transmission from the elastic material. The exosuit and its attachment to the elastic material must be secure, durable, and comfortable. Additionally, the suit should be adjustable and capable of withstanding cyclical fatigue stress generated by the gait cycle. To meet these requirements, we employed an iterative design process guided by a rapid prototyping framework and continuous performance evaluation, allowing us to converge on a refined and optimized final prototype. The resulting design consists of a posture corrector and compressive thigh sleeves. Iterative prototyping and testing informed the selection of a high-strength attachment pattern for securing the HRSL’s elastic material. Adjustable lacing at the thigh seams allows for user-specific compression, ensuring a secure yet comfortable fit across a wide range of body types. This exosuit prototype will support HRSL’s upcoming experimental studies exploring the efficacy of using non-linear elastic materials to reduce energy expenditure during high-speed running.