This study reports the physicochemical characterization and structure–property relationships of rigid sheep wool/phenolic novolac panels developed as bio-based thermal insulation for building envelopes. Mixed Polish sheep wool was washed, mechanically opened, and formed into nonwoven mats, then impregnated with either neat or flame-retardant novolac resin to obtain lightweight boards with a fiber content of about 50 wt%. Elemental analysis, ICP-OES, FTIR spectroscopy, and laser and electron microscopy were used to evaluate the fiber composition, keratin structure, morphology, and fiber–matrix interfaces. Mechanical performance under three-point bending and shear, differential scanning calorimetry, thermogravimetric analysis, and transient hot-probe thermal-conductivity measurements were applied to link microstructure with functional behavior. Novolac impregnation transformed the compliant wool mat into self-supporting panels, increasing the flexural modulus to the 0.8–1.4 GPa range and flexural strength to approximately 48–52 MPa, while the shear modulus and work to failure rose by more than an order of magnitude relative to the loose wool reference. Thermal conductivity remained in a typical range for natural-fiber insulations (λ = 0.061 W·m⁻¹·K⁻¹ for the wool mat and 0.071–0.074 W·m⁻¹·K⁻¹ for the composites), although higher than that of expanded polystyrene. DSC and TGA confirmed that wool fibers remain thermally stable up to about 200–220 °C, that the novolac resin cures around 140 °C, with typical phenolic reaction enthalpies, and that both formulations generate high char residues of roughly 60–80 wt% at 600 °C under nitrogen, evidencing a strong charring propensity rather than directly quantifying fire resistance. Overall, the results position sheep wool/novolac panels between conventional bio-based insulation and structural composites and highlight their potential as sustainable, circular insulation materials for energy-efficient building envelopes.

Low-grade sheep wool is an underused, keratin-rich by-product whose cystine-derived sulphur could be returned to agricultural soils. Carded wool was bonded with sprayed poly(lactic acid) (PLA) hot-melt to obtain porous wool–PLA biocomposite mats, which were exposed in field soil, in a pasture-grass composter and under soil-free outdoor conditions. The elemental composition of the wool, soil, forage, composting material and exposed mats was determined by ICP-OES after 60 days of exposure; each reported value is the mean of at least three analytical determinations, whereas the field layout comprised one plot per treatment. Forage from the plot with buried mats contained 47.8% more S and 21.9% more K than forage from the untreated plot, whereas Ca, Mg, B and Mo concentrations were lower; because the plots were not replicated, these differences are reported as preliminary observations rather than as demonstrated treatment effects. After composting, the mats retained only 17–23% of their initial storage modulus between −30 and 50 °C, while the relaxation of the PLA phase shifted by 7–10 °C towards higher temperatures. The water contact angle decreased from 72.3 ± 10.0° to 55.7 ± 12.1° (six droplets on one mat per condition), while the stylus roughness did not change appreciably. Digital microscopy revealed swelling, fissuring, cavities and fibre exposure along wool–PLA interfaces. A coupled mechanism of PLA ester hydrolysis and keratinolytic release of sulphur is proposed as a working hypothesis that is consistent with, but not yet proven by, the present data. The results support wool–PLA mats as temporary, degradable carriers of keratin-bound sulphur; replicated field trials with yield, nutrient uptake and soil measurements, together with direct degradation markers, are required before any fertilising or soil-improving effect can be claimed.