We characterized the tensile properties of five mid-urethral slings relative to the Gynecare TVT. Slings were divided and loaded to failure. The heat-sealed Boston Scientific mid-section and the American Medical Systems (AMS) tensioning suture were examined separately. Analysis of the resulting nonlinear load elongation curves included calculation of low and high stiffness, the transition point between them (inflection point), load at failure, and relative elongation. Permanent elongation was measured after repetitive loads. Mean values were compared using a one-way analysis of variance. The curves of the Gynecare, Boston Scientific (no midsection) and AMS (no suture) were nonlinear with similar low stiffness and inflection points. The Bard, Caldera, and Mentor slings were stiffer. Heat sealing the Boston Scientific mid-section increased stiffness, while the AMS suture had negligible effect. Cyclical loading induced permanent elongation that was similar for Gynecare, AMS, and Boston Scientific (without mid-section) and lower for Bard, Caldera, and Mentor. With the exception of AMS, the overall effect of newer sling modifications was an increase in tensile stiffness.