<p>Pure sodium alginate (SA) films exhibit high brittleness and elastic modulus, limiting their practical applications. Plasticization with additives, such as glycerol, enhances film flexibility, but conventional solvent casting and evaporation methods limit scalability. Thermo-mechanical mixing has been explored as an alternative; however, it can cause thermal degradation and plasticizer migration, leading in poor film formation and reduced film ductility. In this study, SA-glycerol-water blends were fabricated using mechanical mixing without thermal input. The effects of glycerol and water content on the mechanical, thermal, and barrier properties of the blends were systematically investigated. Elongation at break increased with glycerol content up to 70% of SA mass, while further additions did not improve flexibility. Water acted as a gel-forming medium, modulating mechanical performance alongside glycerol. Optimized blends could be molded into various sizes and shapes, and post-molding dehydration and crosslinking enhanced tensile strength up to tenfold without compromising shape retention. FTIR and DSC analyses indicated strong hydrogen bonding among glycerol, water, and alginate and improved chain mobility. The films exhibit water vapor permeation values within suitable range for packaging application. This approach provides an energy-efficient and scalable route to flexible, moldable, and biodegradable SA-based composites for sustainable packaging and food-based applications.</p> Graphical Abstract <p></p>