This study is dealing with the friction yarn formation process, where the fiber fleece is transformed into a bundle. The bundling procedure can be thought of as the fiber stapling and rolling on the friction drum, of which the dynamics can be described on the basis of the mass conservation. On the basis of the dynamic model obtained the bundle thickness on the friction drum was simulated according to the step and sinusoidal changes in the input fleece thickness. Results showed that the bundle radius response to the step change of the input fleece thickness can be approximately described with the characteristics of an integrating system with the amplitude limit. The sinusoidal change of the input fleece thickness yielded the bundle radius change that depended on the input change frequency. Under certain frequencies of the input fleece thickness change the yam take-up speed could amplify the output yam irregularity, which confirms the possible existence of the process resonance.