ICBBM 2025 in Rio de Janeiro: A synthesis of recent advances, current gaps and emerging directions in bio-based building materials

The 6th International Conference on Bio-Based Building Materials (ICBBM 2025), held in Rio de Janeiro in June 2025, was the first edition organised outside Europe and reflected the growing internationalisation of the field. The proceedings, published in RILEM Bookseries Volumes 60 and 61, gather 144 peer-reviewed papers across eleven thematic sessions covering manufacturing, natural fibres, innovative binders, durability, modelling, environmental assessment, structural applications, earth construction and hygrothermal behaviour. This Technical Letter provides an editorial synthesis of the conference and critically analyses the maturity of the different research areas, the contradictions between studies and the gap between demonstrated evidence and stated claims. Nine structural gaps are identified, including long-term durability, harmonisation of life-cycle assessment and biogenic-carbon accounting, standards and codes, biological variability and building-scale demonstration. The paper also discusses future research trajectories and repositions bio-based construction as an engineered carbon-storage technology with implications for durability, certification and climate mitigation.