Capillary flow is studied in polyester and polyamide yams and glass fibers using a technique based on the analysis of CCD images taken during the capillary rise of colored liquid in yams. The transition from dry yam to wet yam is not abrupt. Experiments analyze the causes of this gradually rising liquid front and the results are explained. As expected, the kinetics of capillary rise always follows the Lucas-Washburn equation, but the great dispersion of the experimental results along the yams is attributed to the yarn heterogeneity of the interfilament space.