The study deals with the mechanical behaviour of a glass plain weave composite reinforcement. The experimental activities were focused mainly on uniaxial and biaxial extension tests. Besides, in-plane shear deformation was measured by bias extension test, and for the sake of completeness out-of-plane bending behaviour. In the numerical study, a hyperelastic constitutive model for the yarn material was adopted and validated for the meso scale prediction of the mechanical behaviour of the glass plain weave reinforcement. The model was validated for biaxial tensile and in-plane shear deformation.