Due to the lack of calibration standards, High Volume Instruments (HVI) does not provide consistently accurate fiber elongation data. In this study, cotton fibers bundle elongation and tenacity were measured using a modified Instron instrument to which Pressley clamps (1/8” gage length) were adapted. Thirty two cotton genotypes with a range of bundle tenacity and elongation were carefully selected based on their distinct physical properties. The work of rupture was calculated for each cotton from the curves Load versus Elongation. Results demonstrated the importance of fiber bundle elongation in the work of rupture of both fiber bundles and yarns, which are critically important to processing performances. This study lays the foundations for future efforts to calibrate the HVI elongation measurements and to breed new lines with improved work of rupture. This should result in lower fiber breakage when the cotton fibers are submitted to different mechanical stresses (ginning, carding, spinning, and weaving)