The objective of this study is to investigate a novel methodology for the in situ light resin transfer molding manufacturing of sandwich panels in which the poly(ethylene terephthalate) foam core is reinforced by transverse polymeric pins used to improve both flatwise compressive and flexural strength of the foam. The foam cores were pre-drilled, and these holes were later filled with resin during the light resin transfer molding production of the panels. Five types of samples were evaluated: control (core without pins) and reinforced cores with variable pin diameters and distances. Both experimental and numerical results are presented, and good agreement between them was achieved. Pin diameters below 3 mm lead to failure by local buckling, whereas diameters larger than 4 mm showed manufacturing issues related to the incomplete formation of pins.