Advanced air, land, and sea based vehicle applications requiring high strength and low weight often utilize sandwich panel structures consisting of stiff facesheets and a low density core. Current manufacturing techniques limit core geometries to highly symmetric configurations. Many of these limitations are removed with the use of fused deposition modeling (FDM). Furthermore, electroforming over the model material can be used to dramatically increase the mechanical properties of the parts. This work presents the characterization of three core topologies, tetrahedral, pyramidal, and strutreinforced tetrahedral (SRT) that were optimized for specific strength. The response of fused deposition acrylonitrile butadiene styrene (ABS) plastic and electroform coated ABS cores is presented. The SRT exhibited superior performance in yield strength, ultimate strength, and energy absorption.The demand for faster and more economical air, land, and sea vehicles requires increased weight efficiency. Sandwich panels are commonly used in advanced material systems for weight critical applications. Sandwich panels provide high specific strength and stiffness, making them ideal structures for these engineering applications. The core of the sandwich panel is critical to performance but current core geometries are limited to those manufactured using stochastic foaming processes, [1,2] deformation processes, [3][4][5][6][7][8] and pin insertion techniques. [9][10][11] Wadley et al. [12] presented a review of deformation processes which generate periodic arrays such as pyramidal, [4,7] woven, [5,[13][14][15] tetrahedral, and corrugated cores. [6,16] Additionally, pinning can be used to produce cores with symmetrical or asymmetrical geometries. [9][10][11] Work by Kooistra et al. [17] has suggested that emerging core topologies with higher stiffness and strength efficiency metrics exist but manufacturing limitations prevent full optimization of the core geometries. Rapid prototyping has been embraced by the design and manufacturing community due to its efficiency and ability to produce complex geometries which cannot be developed effectively using traditional machining and manufacturing techniques. Specifically the FDM process generates an ABS plastic structure from a CAD model. The theoretical cores proposed by Deshpande et al. can readily be produced using rapid prototyping techniques. [18] The ability to produce any core geometry, within the tolerance of the machine allows the theoretical cores to be validated.Cores produced from ABS plastic suffer from the limited mechanical properties of ABS. However, work by Burns et al. suggests that electroforming ABS materials with copper and nickel increases the yield strength four-fold and the elastic modulus by up to 15 times making the composite mechanically competitive with structural materials. [19] Electroforming is a technique, like rapid prototyping, which can be used on complex geometries. Electroforming the ABS cores may increase the strength and stiffness of ABS cores making the FDM/...