A new method for fiber flexibility measurement has been developed using confocal laser scanning microscopy (CLSM), based on the fiber conformability method. Freespan length was measured directly from the transverse view of the fiber span, so the accuracy of the measurement was greatly improved. The collapsibility and moment of inertia can also be measured from the fiber cross section obtained from CLSM. Thus, it was possible to measure the elastic modulus of individual fibers. Therefore, all the basic properties of fiber that affect its conformability, including fiber wall thickness, moment of inertia, and elastic modulus, can be measured within a single test. Results show that both fiber collapsibility and the elastic modulus of the fiber wall affect the fiber flexibility. Collapsibility is controlled mainly by fiber wall thickness. A refining or bleaching process can increase fiber flexibility mainly by altering fiber elastic modulus.