Dynamics of the bundle thickness in a friction yarn formation process was ascertained experimentally from the view point of the thickness of in-process bundle and output bundle. By changing the thickness of input fleece the thickness distribution of the in-process bundle on the friction drum and the irregularity of the output bundle in a steady state were measured. The experimental results were then compared with the simulation results derived on the basis of the dynamic model, while a step signal and a sinusoidal signal were applied. Experimental results turned out to be in a good agreement with the simulation result, which indicates that the theoretical model describes the dynamics of the frictional bundling process very good. The cross-sectional area of the in-process bundle increased linearly to the drum position in response to a step change in the input fleece thickness, which indicates that the friction bundling process can be though of as an integrating system with an interval. The periodic change in the input fleece thickness yielded also a good correspondence of the experimental results with those from the simulation. However, the thickness behavior of the output friction yarn for the periodic change in input fleece thickness demonstrated the dependency on the take-up speed of the output bundle.