<p>Lightweight industrial and commercial construction projects are increasingly employing hollow cold-formed steel (CFS) sections. Still, their overall capacity to withstand forces during flexure may be significantly impacted by potential forms of buckling failure. Hollow CFS sections can significantly enhance the overall performance by mitigating local inward buckling, while concrete functions as filler materials. This study examines the viability of lightweight foam concrete (LFC) as an infill material for hollow beam sections subjected to flexural loading. The infill material's density was maintained between 800 and 1900 kg/m³. Screw spacing, section thickness, and filling property are among the important characteristics studied. Eight cold-formed steel beams with a total span of 2500 mm are fabricated and evaluated as part of the comprehensive experiment. The experimental program includes figuring out the beams' (both hollow and infilled) ultimate strength, stiffness, failure mechanisms, and load-deflection behavior. Furthermore, the ABAQUS program was employed to conduct a comprehensive nonlinear finite-element (FE) analysis. The theoretical flexural capacity of hollow CFS built-up beams was computed using the direct strength method (DSM) in accordance with AISI S100-2012. For infilled sections, an empirical extension of DSM was adopted to account for the influence of foamed concrete. Compared with hollow specimens, the test results indicated that LFC infill increased ultimate moment capacity by 34.8% and stiffness by more than 100%. Additionally, the use of LFC infill greatly increases the local buckling resistance of hollow CFS sections.</p>