The penetration of CMC solutions and coating liquids into paper sheets was investigated experimentally and modeled using a Lucas-Washburn equation (Lepoutre, 1978) adequately modified to account for the dynamic contact angle and the coating fluid theology. A numerical simulation of the fluid penetration based on the finite element resolution of the Navier-Stokes equations was carried out as well. The numerical predictions and the predictions of the Lucas-Washburn equation were compared with the experimental data showing the limitations of the models.