Sheep wool is a keratin-based natural fiber increasingly explored as a low-impact reinforcement and multifunctional modifier in composites, enabling valorization of coarse or waste wool streams. This systematic review consolidates evidence on raw or minimally processed wool-reinforced composites across polymer matrices and mineral binders. Following a registered protocol and Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020, Scopus and Web of Science were searched for English-language journal articles (2015–2025), yielding 44 included studies after screening. Evidence mapping shows polymers dominate (33/44; thermosets 19/44), while mineral binders account for 11/44. Wool is mainly used as short fibers (27/44), with woven (9/44) and nonwoven/felt (8/44) architectures appearing in laminates and insulation products. Because heterogeneity limits pooled meta-analysis, outcomes are synthesized using matched-control comparisons where available (27/44) and interpreted with a TRiC appraisal (Transparency, Reproducibility, and Credibility). Mechanical effects are highly conditional: gains in impact/energy absorption and occasional tensile/flexural stress improvements coexist with frequent losses linked to dispersion, wetting/impregnation and void sensitivity. Functional trends are similarly system-dependent, with promising but uneven evidence for acoustic performance, variable thermal conductivity shifts, and formulation-driven fire behavior. Moisture uptake and durability emerge as principal translation bottlenecks, motivating minimum reporting and design practices to improve comparability and application readiness.
Ruiz-Díaz et al. (Mon,) studied this question.