Processing–structure–property relationships in PS–SiO2 nanocomposite foams: a comparative study of batch and extrusion foaming for thermal insulation applications

Polystyrene (PS) foams are widely used as thermal insulators; however, further improvements in their performance require control of their cell size and scalable manufacturing strategies. Nanosilica (SiO 2 ) was proposed as an effective nucleating agent in laboratory-scale batch foaming. Yet, a knowledge gap remains regarding how nanosilica influences foam morphology in a continuous and industrially relevant technology as extrusion foaming. In this work, PS-SiO 2 nanocomposite foams were produced through two routes –batch and extrusion foaming– to establish process–structure–property relationships. Results show that nanosilica reduces cell size in both processes, with strong differences. Batch foaming induces a higher nucleation, resulting in microcellular structures (2–5 µm) with high open-cell content. Conversely, extrusion foaming yields foams with larger (100–200 µm) closed cells. These structures lead to contrasting mechanical responses, with the extruded nanocomposite foams showing enhanced performance over pure PS. Overall, both processes enable the fabrication of advanced thermally insulating materials, while highlighting the decisive role of the foaming process in the effectiveness of nanosilica. Open-cell microcellular foams produced via batch foaming are promising candidates for vacuum insulation panels (VIP), achieving thermal conductivities in the super-insulation range, while the extruded foams offer improved insulation due to reduced radiative heat transfer.