The flexural behavior of a beam is investigated in an attempt to establish a correlation between tension, compression stress strain model and bending properties of polymer materials. Given the complete uniaxial stress strain relations including the post peak response, it is possible to predict the flexural behavior in moment curvature relations. A constitutive law for tension and compression of resin polymer material is proposed. The model consists of constant flow in tension and constant yield in compression in post peak regions. The model is described by two main parameters; modulus of elasticity in tension and strain at the proportional elastic limit point in tension, in addition to nine non-dimensional tension and compression parameters. Closed form equations for moment curvature relationship are presented. Moment curvature response was obtained from flexural three point bending tests using optical measurement technique. Results showed the robustness of the proposed model to predict the flexural response.