Physicochemical and hygrothermal characterization of loose-fill wheat straw for building insulation

Bio-based insulation materials are receiving increasing attention as sustainable alternatives to conventional building materials. Wheat straw is widely available in agricultural regions and has mainly been studied in bale form or as part of composite materials, while its use as a loose-fill material for blown-in insulation remains less documented. Unlike composites, loose-fill straw does not require a binder, and compared with bales, it can be more easily applied in closed cavities and complex building geometries. This makes it a flexible, binder-free and fully bio-based insulation material. However, its performance depends on specific material parameters, such as particle size, density and porosity, which need to be better understood for reliable use in buildings. This study examines the physicochemical, hygroscopic, and thermal insulation properties of eight batches of loose-fill wheat straw available in France. The material was characterized through several analyses, including chemical composition, particle size distribution, density and porosity, fire reaction tests, moisture buffering capacity, sorption behavior, thermogravimetric analysis, thermal conductivity, and specific heat capacity. The results show that some differences exist between batches, but the general behavior of the material remains similar. The processed straw presents very high porosity, moderate to good moisture buffering capacity and thermal conductivity values ranging from 0.0435 to 0.0526 W·m⁻¹ ·K⁻¹ , confirming its good thermal insulation performance. The sorption behavior of the samples was well described by the GAB and BET models, and thermal analysis also showed a degradation behavior typical of lignocellulosic materials. Overall, these results indicate that loose-fill wheat straw has suitable properties for building insulation and could be considered a promising bio-based alternative for blown-in insulation systems.