This work presents the results of experimental and numerical analyses of the static properties of architectural cores and the dynamic behavior of sandwich structures made with an auxetic or non-auxetic core. Three architectural cores have been studied which are re-entrant, rectangular and hexagonal honeycombs. Each configuration was produced with four relative densities depending on the number of cells in the width of the specimens. The specimens were made with additive manufacturing technology. The material used to make the specimens was polylactic acid with flax fibers. Several tensile tests were carried out on the architectural cores to analyze and understand the influence of the topology and the density of the core on the Poisson’s ratio and the Young’s modulus of these architectural structures. Then, vibration tests were carried out on the cores and the sandwich structures. The objective was to study the influence of these structures and their densities on the dynamic properties of sandwiches. The structural Poisson’s ratio shows a sensitive behavior to the core topology and density.