Sandwich Panels with cellular cores are widely used in the aerospace industry for their higher stiffness to mass, strength to mass ratio, and excellent energy absorption capability. Even though, sandwich panels are considered state of the art for lightweight aerospace structures, the requirement to further reduce the mass exists due to the direct impact of mass on mission costs. Traditional manufacturing techniques have limited the shape of the cores to be either hexagonal or rectangular, but, with rapid advancements in additive manufacturing, other core shapes can now be explored. This research aims to identify and evaluate the mechanical performance of two-dimensional cores having standard wall geometry, which provide higher specific stiffness than honeycomb cores. Triangular cores were identified to have higher specific in-plane moduli and equivalent specific out-of-plane and transverse shear moduli. To consider practical use of the triangular cores, elastic and elastic-plastic structural analysis was performed to evaluate the stiffness, strength, failure, and energy absorption characteristics of both the core and sandwich panels. The comparison made between triangular cores and hexagonal cores having the same cell size and relative density showed that triangular cores outperform hexagonal cores in elastic range and for applications where in-plane loading is dominant. Triangular cores also have excellent in-plane energy absorption capabilities at higher densities. / Master of Science / Sandwich panels with cellular cores are widely used in aerospace structures to reduce weight, which helps increase payload and improve fuel efficiency. They also have the ability to absorb energy during accidental impacts. Sandwich construction typically consists of two thin facesheets separated by a lightweight core and, is analogous to I-beams used in civil structures. Most commonly used core is the hexagonal honeycomb core inspired by beehives. While sandwich panels constructed using honeycomb cores are considered the state-of-the-art for lightweight aerospace structures, there is a need to further reduce the mass due to the direct impact on mission costs. This research aims to explore other core shapes that provide better stiffness to mass ratio than the hexagonal core. Among the two-dimensional cores explored, the triangular shaped core was identified to have higher stiffness than the hexagonal core of the same size and weight. To consider practical use of triangular cores, mechanical performance and failure behavior of sandwich panels constructed using triangular core sandwich panels was compared to hexagonal core sandwich panels. It was concluded that the triangular panels provided higher stiffness for the same mass and was more resistant to failure when axially loaded. Triangular cores also have excellent in-plane energy absorption capabilities at higher densities.