A new method has been developed for estimating the modulus and toughness of cotton fiber bundles directly from the HVI tenacity-elongation curves. The bundle modulus and toughness were obtained for 36 U. S. Upland cottons from the 1995 crop. The HVI properties including bundle modulus and toughness, Mantis^® single fiber tensile properties and yarn tenacities were analyzed to evaluate the relationship among fiber , bundle and yarn properties. The single fiber tensile properties were shown to be translated well into the bundle tensile properties. The single fiber breaking elongation was found to be the most significant contributing factor to bundle tensile properties. The bundle breaking elongation and toughness were shown to increase as the single fiber breaking elongation increased. The bundle modulus increased as the single fiber breaking elongation and/or standard deviation of single fiber breaking elongation decreased.