The MANSART project, for "architectured sandwich materials", aims at developing innovative architectured materials, exhibiting improved functional properties in comparison with traditional composites. Our contribution is focused on modeling and simulation of architectured microstructures, prediction of their effective properties using numerical homogenization implemented with finite elements (Z-set software). Rapid prototyping using selective laser melting allows us to fabricate samples and validate the numerical prediction. Two types of morphologies have been identified: randomly distributed entangled Poisson’s fibres and auxetic periodic lattices. Effective properties of Poisson’s fibres is investigated although estimation is challenging since statistical representative volume element (RVE) size is a priori unknown, due to an infinite integral range as shown in [Jeulin, 1989]. Scaling laws for variances of properties are computed. Auxetics are architectured materials exhibiting a negative Poisson’s ratio. Mechanical behavior of such materials is investigated for both elastic and plastic domains. 2D and 3D lattices are proposed for industrial applications.