A computer model was developed which makes it possible to predict the effects of several cigarette properties on the different degrees of ventilation (total degree of ventilation, degree of ventilation of the tobacco rod, degree of ventilation of the filter) and on the pressure drop. A special advantage of this model is its ability to predict the degree of ventilation from the properties of the materials (e.g. of filter, paper, tobacco) instead of from the properties of the manufactured cigarette. Thus it is no longer necessary to manufacture an experimental cigarette each time. Another advantage results from the fact that the fluctuations of the degree of ventilation can be attributed directly to the factors responsible. Each contribution of the individual factors responsible can be determined separately, which is normally not possible by means of experiments. Thus this model is not only a component of a computer-aided product design, but is also a useful tool for quality control. Some examples are presented which are typical of the effects of various properties of the materials on the ventilation. It becomes obvious that a low level of fluctuations of the filter ventilation does not only imply constant properties of the applied materials (such as tipping paper) but also a uniform primary process.