The new materials belong to a class known as mycelium biocomposites, in which the vegetative root-like networks of fungi are grown through organic substrates such as agricultural residues. The fungal hyphae bind the loose lignocellulosic particles into a solid, relatively lightweight structure that is biodegradable and recyclable. Historically an experimental biomaterial, mycelium composites have attracted growing attention because of their promising combination of low weight, thermal insulation capacity, and reasonable strength and durability. Their production also offers a route to valorizing by-products, storing atmospheric carbon dioxide, and reducing dependence on petrochemicals, all while embodying circular economy principles in which materials can be disassembled, reused, and ultimately returned to natural systems.

Producing these composites is a multi-phase biological process rather than an industrial extrusion. Mycelium is first grown on a substrate over one to two weeks under carefully controlled conditions, typically at temperatures between 24 and 30 degrees Celsius and humidity levels of 60 to 75 percent. The material then develops for two to four weeks as the fungal network colonizes the substrate into a uniformly dense structure. A final drying stage, lasting from a few days to a week, halts fungal growth and provides the strength and dimensional stability that make the material usable in construction. Each of these steps, along with the choice of substrate and fungal strain, shapes the physicochemical characteristics of the finished composite.

In the new study, a research team prepared four experimental series of mycelium biocomposites, each with a different composition, production flow, and specimen geometry. Series I combined wheat straw with Ganoderma lucidum, Series II paired flax straw with Pleurotus ostreatus, Series III used hemp shives with Pleurotus ostreatus, and Series IV tested wheat straw, hemp shives, and flax straw, each inoculated with Ganoderma lucidum. All samples were produced by mixing 7.5 grams of colonized grain spawn into 300 grams of sterilized straw, a spawn-to-substrate ratio of 2.5 percent, with the sterilized substrate held at approximately 60 percent preparative moisture. The mixtures were compressed by hand into cardboard molds shaped as cubes, cylinders, or rectangular prisms, then cultivated and dried under formulation-specific conditions before testing.

The team evaluated four parameters most relevant to insulation performance: thermal conductivity, density, flexural strength, and compressive strength. Density was measured with a precision laboratory balance and manual dimensional measurements, while thermal conductivity was assessed with a portable Isomet 2114 heat transfer analyzer under controlled laboratory conditions of 20 degrees Celsius and 50 percent relative humidity. Each specimen was measured twice on adjacent surfaces, with the median value used for analysis. The researchers also computed a thermal conductivity-to-weight ratio, an inverse indicator that favors formulations combining low heat conduction with low bulk density, to compare the overall thermal-mass balance of the tested materials.

The results revealed striking differences among the formulations. Thermal conductivity ranged from 0.0385 to 0.0719 watts per meter-kelvin depending on substrate and fungal strain, while densities spanned from 80 to 227 kilograms per cubic meter. The standout performer was the hemp shive composite inoculated with Pleurotus ostreatus, which achieved the lowest density range of 80 to 120 kilograms per cubic meter and the most efficient thermal conductivity, from 0.0385 to 0.057 watts per meter-kelvin. This formulation recorded the highest thermal conductivity-to-weight ratio of 0.209, approximately 35.7 percent higher than the next best formulation in the study. By contrast, the multi-material Series IV showed the widest variability in both density and conductivity, reflecting the challenges of consistency in mixed compositions.

Mechanical testing of the optimal hemp shive and Pleurotus ostreatus composite produced equally notable results. Two independently molded prism specimens, each 40 by 40 by 160 millimeters, were subjected to three-point bending on a standardized flexure testing device with a 100-millimeter support span. The composite achieved an average flexural strength of 8.85 megapascals, with individual specimens reaching 8.58 and 9.11 megapascals. Compressive testing on the uncracked halves of the broken prisms yielded an average compressive strength of 4.25 megapascals. Both values exceed or match similar mycelium-based composites described in the literature, where flexural strengths have typically ranged from 0.44 to 4.23 megapascals depending on substrate, and many lignocellulosic formulations have shown compressive strengths below 1 megapascal.

To contextualize these findings, the researchers benchmarked their data against seven published studies of mycelium composites made from comparable plant-derived substrates, plotting thermal conductivity jointly with density because porosity and density strongly influence thermal performance. The literature dataset spans roughly 0.035 to 0.096 watts per meter-kelvin across a wide density range. The hemp shive composite’s minimum conductivity of 0.0385 watts per meter-kelvin compares favorably with values reported for birch sawdust composites and mycelium-bound fibers from invasive plants, and its combination of approximately 100 kilograms per cubic meter density with low conductivity places it firmly in the favorable low-density, low-conductivity region of the performance map. The authors caution, however, that differences in specimen geometry, moisture state, processing conditions, and measurement procedures mean such comparisons serve as performance benchmarking rather than a strictly standardized ranking.

The researchers supplemented their measurements with scanning electron microscopy of the wheat straw and Ganoderma lucidum formulation, which revealed an interconnected filamentous network bridging the lignocellulosic structural elements and numerous micrometer-scale voids. These images provide qualitative evidence of the porous microstructure that underpins the materials’ insulating behavior, although porosity was not quantitatively determined. The team also conducted a rigorous uncertainty analysis, estimating measurement-related uncertainties of roughly 0.6 to 1.3 percent for density, 6.4 to 7.6 percent for thermal conductivity, 3.0 percent for flexural strength, and 2.0 percent for compressive strength, ensuring the reported values rest on a transparent methodological foundation.

The implications extend beyond the laboratory. The hemp shive and Pleurotus ostreatus composite appears suitable for non-load-bearing panels, partition walls, insulation boards, and lightweight structural components, applications where its combination of insulation efficiency, mechanical cohesion, and biodegradability offers genuine advantages over conventional materials. The authors emphasize that their mechanical values rest on limited replication and that future work must address scalability, fire behavior, moisture resistance, biological durability, ageing, dimensional stability, and industrial-scale manufacturability before building-scale deployment. Nevertheless, the study provides practical guidance for future research, industrial pilot projects, and policy-driven adoption of eco-composites. As the construction sector confronts its outsized carbon footprint, materials grown from fungal networks and farm waste are moving from curiosity toward credible contender, proving that the walls of future buildings might one day be cultivated in a matter of weeks.

Subject of Research: Thermal and mechanical performance of mycelium-agricultural waste biocomposites for building insulation

Article Title: Mycelium–Agriwaste Biocomposites for Cleaner Building Insulation: Thermal and Mechanical Performance

Article References: Babenko, M., Kononets, Y., Kunes, R., Makys, P., Spalek, F., Sramhauser, K., Hanzal, P., Majernik, J., Zoubek, T., & Bartos, P. (2026). Mycelium–Agriwaste Biocomposites for Cleaner Building Insulation: Thermal and Mechanical Performance. Cleaner Engineering and Technology, Article 101334. https://doi.org/10.1016/j.clet.2026.101334

Image Credits: AI Generated

DOI: 10.1016/j.clet.2026.101334

Keywords: mycelium biocomposites, building insulation, hemp shives, Pleurotus ostreatus, Ganoderma lucidum, thermal conductivity, agricultural waste, sustainable construction, circular economy, flexural strength, compressive strength, lignocellulosic substrates

Hemp shives, the woody core of the hemp stem left over after bast fibers are harvested, are an attractive raw material. They are lightweight, highly porous, and offer thermal conductivity around 0.048 W/m·K, making them excellent candidates for insulation panels. When bonded with gelatinized potato starch, hemp-shive composites have previously achieved thermal conductivities in the range of 0.06 to 0.07 W/m·K and impressive moisture-buffering values above 2.6 g/(m²·%RH). But the same porosity that makes them good insulators also makes them vulnerable. Water seeps into the open pore network, the hydrophilic starch binder swells, and over time the material can lose dimensional stability, mechanical integrity, and resistance to biological growth.

Earlier attempts to fix this weakness have relied on thermal modification of fibers, silane treatments, hot-water extraction, or synthetic hydrophobic coatings. These approaches work, but they add processing steps, energy demands, costs, and sometimes environmentally questionable chemistry. The new study takes a different route: instead of chemically altering the plant material, the researchers simply dispersed finely ground natural calcium carbonate throughout the matrix. The mineral powder, milled from Champagne-region limestone and composed of 94.6 percent calcium carbonate, was treated not as a passive filler but as a functional additive that reshapes the composite’s internal architecture.

Because the performance of such composites depends on several competing variables, the team avoided trial-and-error formulation. They applied Response Surface Methodology using a Central Composite Design, varying two parameters, the starch-to-fiber ratio and the calcium-carbonate-to-fiber ratio, across eleven experimental runs including replicated center points. Four responses were tracked simultaneously: bulk density, thermal conductivity, water absorption, and compressive strength. Quadratic regression models fitted to the data achieved coefficients of determination between 0.83 and 0.94, and analysis of variance confirmed that both factors and their interaction significantly shaped every property measured.

The models revealed a fascinating tug-of-war inside the material. Increasing starch raised water uptake, as expected from its hydroxyl-rich chemistry, but calcium carbonate pushed hard in the opposite direction, blocking capillary pathways and reducing the accessible internal surface. A significant negative interaction term showed that the mineral partially counteracts the binder’s hydrophilic tendency. Meanwhile, both components boosted compressive strength, with starch dominating through inter-particle bonding and calcium carbonate acting as a micro-reinforcement that stiffens the matrix and fills residual micropores. Density and thermal conductivity rose moderately with both additives, a predictable consequence of replacing trapped air with solid matter.

Multi-objective optimization using desirability functions converged on a formulation with a starch-to-fiber ratio of 0.30 and a calcium-carbonate-to-fiber ratio of 0.39. Validation experiments matched the predictions closely, with individual errors of 0.93 to 6.46 percent and an average deviation of just 3.72 percent, yielding a global desirability of 80 percent. The optimized composite reached a bulk density of 221 kg/m³, a thermal conductivity of 0.056 W/m·K, water absorption of 22 kg/m², and a compressive strength of 0.68 MPa, a compelling balance of insulation, strength, and moisture resistance.

Microscopy and porosimetry explained why the formulation works so well. Scanning electron micrographs of the reference material showed a heterogeneous, poorly bonded structure with large voids and smooth, uncoated hemp particles. In the optimized composite, calcium carbonate microspheres were embedded throughout the matrix, the binder film became continuous and evenly distributed, and fiber-matrix interfaces appeared far more cohesive. Mercury intrusion porosimetry quantified the transformation: total intrusion volume fell from 2.635 to 1.577 mL/g, total porosity dropped from 73.5 to 66.0 percent, and the median volumetric pore radius shrank from 0.452 to 0.401 micrometers. Ultrasonic pulse velocity nearly doubled, rising from 273 to 446 m/s, confirming dramatically improved internal cohesion.

The hydric results were equally striking. Capillary water absorption at long exposure times fell by roughly 29 percent compared with the references, from more than 30 kg/m² to 22 kg/m², and the wetting front penetrated only about 5 centimeters into the optimized panel. Surface wettability improved as well: the initial water contact angle climbed from around 50 to 54 degrees for the references to 87.26 degrees for the optimized composite, and the starch-calcium-carbonate binder gel itself showed a higher contact angle than pure starch gel. Crucially, the material did not become a vapor barrier. Water vapor permeability remained in the same range as other plant-fiber insulators, and the moisture buffer value actually reached the classification of excellent, meaning the wall material can still absorb and release humidity to regulate indoor air, while resisting liquid water ingress.

Acoustic and thermal stability tests rounded out the picture. Sound absorption curves for all formulations showed a characteristic peak near 1000 Hz, and the weighted absorption coefficient slightly improved from 0.30 to 0.36 with the mineral addition, indicating that pore refinement did not destroy the interconnected network responsible for acoustic dissipation. Thermogravimetric analysis showed the optimized composite retained 37.1 percent residual mass at 600 °C, compared with under 21 percent for the references, thanks to the mineral fraction and the endothermic decarbonation of calcium carbonate near 770 °C. Infrared spectroscopy confirmed the diagnostic carbonate bands in the optimized sample and suggested interfacial interactions, possibly hydrogen bonding, between the mineral surface and the hydroxyl-rich organic matrix.

The broader significance is that a mineral available almost anywhere, requiring no chemical synthesis, can deliver durability improvements that previously demanded elaborate surface treatments. The researchers caution that long-term service performance, including freeze-thaw cycling, wet-dry aging, biological attack, and fire behavior, still requires dedicated testing, and a full life-cycle assessment remains to be done. But the demonstration that ground limestone can simultaneously strengthen a hemp-starch insulation panel, cut its water uptake by nearly a third, preserve its breathability and moisture buffering, and even modestly improve its acoustic and thermal stability marks a meaningful step toward insulation materials that store carbon, breathe with the building, and survive decades of real-world weather.

Subject of Research: Multi-objective optimization of hemp-shive and starch biocomposites reinforced with natural calcium carbonate for moisture-resistant building insulation

Article Title: Natural CaCO₃ improves the moisture resistance and mechanical performance of hemp-starch biocomposites: A multi-objective optimization study

Article References: Balti, S., Maalouf, C., Moussa, T., Bliard, C., Lachi, M., Rousse, C., Alsedeh, O., Vazquez, P., Bogard, F., & Polidori, G. (2026). Natural CaCO₃ improves the moisture resistance and mechanical performance of hemp-starch biocomposites: A multi-objective optimization study. Case Studies in Construction Materials, 25, Article e06574. https://doi.org/10.1016/j.cscm.2026.e06574

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06574

Keywords: hemp shives, calcium carbonate, potato starch, bio-based insulation, response surface methodology, moisture resistance, thermal conductivity, compressive strength, porosity, moisture buffering, sustainable construction, biocomposites