A model describing the relationship between cutting force and cutting speed during cutting operation of fibrous materials was developed. The model was based on analysis of their theological model. The experimental data, obtained during cutting different fibrous materials, were used to estimate the parameters of the model using non-linear parameter estimation. According to the developed model the unit power of the cutting operation of a given fibrous material with a knife of defined geometric parameters is a constant value. (C) 2004 Elsevier Ltd. All rights reserved.