Sheep wool as a sustainable building insulation: a systematic review of properties, environmental impacts and future perspectives

Purpose Sheep wool is re-emerging as a bio-based insulation with promising thermo-acoustic and environmental profiles, but earlier reviews often mixed heterogeneous outcomes and system boundaries. This study addresses those gaps by harmonizing metrics and explicitly declaring comparison rules. Design/methodology/approach We conducted a Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)-guided review (2010–2025) with dual independent screening, covering coupon-scale experiments, commercial products, composites and life-cycle assessments (LCAs). Outcomes were normalized to thermal conductivity at 23 °C and 50% RH, reverberation-room absorption summarised as noise reduction coefficient (NRC) for 50–60 mm panels, and life-cycle indicators expressed per a functional unit (UF) of 1 m2 delivering R = 3.5 m2 K W−1 over 50 years under cradle-to-grave boundaries, with allocation sensitivity when wool is a coproduct. The risk of bias was qualitatively assessed across the reporting and methods domains. Findings After normalization or moisture/density subgrouping, wool exhibited λ values clustering around 0.034–0.048 W m−1 K−1 and NRC typically 0.55–0.90 at 50–60 mm, with variability explained mainly by density, air-flow resistivity and moisture conditioning. Hygrothermal buffering can moderate indoor humidity, but in warm-humid climates requires explicit vapour-control design to limit λ drift. Scenario LCAs indicate lower embodied energy and global warming potential per UF when residual wool is valorized, transport is regional and halogen-free protection is used. However, rankings remain sensitive to allocation, electricity mix and end-of-life routes. Originality/value Under a declared UF and cradle-to-grave boundaries, sheep wool can deliver competitive thermo-acoustic performance with favourable life-cycle profiles. Priorities include 24–36-month tropical field studies, low-hazard moth and flame protection that is compatible with circularity, standardized λ-moisture normalization, NRC reporting at reference thickness and regionalized life-cycle costing.