The efficacy of geofoam buffers in enhancing the seismic performance and dynamic load response of retaining walls and road embankments is well-established. However, limited research has been conducted to comprehend their role in mitigating soil liquefaction. This study investigates the shearing behavior of sands with Expanded Polystyrene (EPS) geofoam buffers, both before and after liquefaction, through a set of monotonic and cyclic simple shear tests. The investigation considers variations in layer thickness and geofoam density, employing two different thicknesses and three different densities in the tests. The results indicate that geofoam buffers reduce both pre-liquefaction and post-liquefaction shear strength of sand. However, they demonstrate a significant improvement in liquefaction resistance, with better outcomes observed at increased layer thickness and lower geofoam density. This enhancement is attributed to the exceptional energy absorption quality and compressibility of geofoam buffers. Nonetheless, this has a converse impact on the shear strength of sand. Consequently, it is imperative to carefully select the appropriate density and thickness of the geofoam layer to strike a balance between shear strength and liquefaction resistance.