In meso-scale finite element modeling, the yams of the reinforcement are considered to be solids made of a continuous material in contact with their neighbors. The present paper consider the mechanical behavior of these yams that can happen for some loadings of the reinforcement. The yams present a specific mechanical behavior when under longitudinal compression because they are made up of a large number of fibers, Local buckling of the fibers causes the compressive stiffness of the continuous material representing the yarn to be much weaker than when under tension. In addition, longitudinal compression causes an important transverse expansion. It is shown that the transverse expansion can be depicted by a Poisson ratio that remained roughly constant when the yam length and the compression strain varied. Buckling of the fibers significantly increases the transverse dimensions of the yam which leads to a large Poisson ratio (up to 12 for a yam analyzed in the present study). Meso-scale finite element simulations of reinforcements with binder yams submitted to longitudinal compression showed that these improvements led to results in good agreement with micro-CT analyses.