Bundle strength of cotton fibers as tested by HVI and Pressley/Stelometer are studied as means for predicting the strengths of yams spun from the same fiber population. Classical bundle strengths are compared against the "true" bundle strengths obtained by superposition of the single fiber load-elongation diagrams generated by an AFIS single fiber testing machine under development. The differences between the two are discussed in terms of the single fiber data and the bundle strength efficiencies corresponding to varying yarn sizes.