Protein‐Based Insulation Foams from Soy Protein Isolate: Influence of CaCl ₂ Addition on Foam Formation and Thermal Performance

Abstract

The development of bio‐based insulation materials requires concepts that combine low apparent density, stable pore structure and sufficiently controlled drying. In this study, duck‐feather‐reinforced soy protein isolate (SPI) foams were produced from aqueous dispersions by thermal stabilisation at 120 °C. The influence of calcium chloride (CaCl ₂ ) dosage was investigated using a broad screening series followed by a refined investigation of the technically relevant range between 50 and 100 mmol CaCl ₂ per 200 g SPI. This approach enabled the identification of a dosage window that provides sufficient matrix stabilisation without excessive salt addition. The resulting foams were evaluated regarding pro‐cessability, thermal conductivity, apparent density and compressive behaviour. Thermal conductivities of approximately 52–53 mW/(m·K) were achieved at mean apparent densities of approximately 210–220 kg/m ³ . The results indicate that foam performance is governed by the interaction of moisture removal, matrix consolidation and pore stabilisation during drying. Future work may extend this approach to other calcium‐based mineral additives to improve drying behaviour, moisture resistance, structural integrity and handling stability in building‐material‐oriented formulations.