In this chapter, we focus on the relationship between fibers' mechanical properties and yarns' ones by studying their relative behavior and the relationship between single and bundle cotton fibers (respectively, dispositions 1 and 2). For this purpose, three different types of cotton fibers were studied. These cottons were chosen from a list of 12 cottons covering a large panel of varieties and physical properties (maturity, fineness, micronaire, length, tenacity, etc.). Classifications per length classes and linear densities were done in order to have more precision and knowledge of cotton fiber behavior. Modeling the creep behavior of single and bundle fibers will help exploring data for the bijective relationship between the two dispositions. Properties evaluated will include elongation, single fibers and bundle tenacities, work of rupture, and so on. Quality of bundle fibers will be a good tool in predicting spinning performances and thus yarn quality.