In this work the experimental observations are explained with the aid of a simple air-entrapment model based on the concept of two levels of porosity of fiber mats, A simple model that includes liquid bypassing with initial air trapping, subsequent capillary invasion of regular fiber bundles with air compression, and finally mobilization is proposed to explain air-entrapment phenomena. The simple model successfully rationalizes the observed air trapping and compression during initial liquid-fiber contact. An empirical equation for the mobilization efficiency is adapted to the model to estimate void content. The velocity dependence of the trapped void content predicted by the model is in good agreement with observations.