Fungi-Based Materials and Indoor Air Quality: What Mycelium Products Can—and Cannot—Prove

Fungi-based materials are products made with fungal mycelium—the network of thread-like hyphae that forms the vegetative body of a fungus—often grown through agricultural fibers and then dried, pressed, or heat-treated. They may reduce reliance on petrochemical foams and plastics, but the claim that they automatically improve indoor air quality is not supported by sufficient building-performance evidence. Indoor results depend on the material’s moisture content, biological stability, surface finish, emissions, installation location, and maintenance. The U.S. Environmental Protection Agency reports that indoor pollutant concentrations can be two to five times higher than outdoor levels, and sometimes much higher, making verification of any new interior product important. The central distinction is that a properly manufactured, dry, and sealed mycelium composite is not the same thing as actively growing mold.

Fungi-Based Materials Influence Indoor Air Quality Through Emissions, Moisture, and Biology

Indoor air quality is the condition of indoor air in relation to occupants’ health, comfort, and ability to perform normal activities. The U.S. EPA evaluates indoor air through pollutants and stressors such as particulate matter, volatile organic compounds, carbon monoxide, allergens, biological contaminants, and excess moisture. Fungi-based materials affect this attribute through three main pathways: chemical emissions, moisture behavior, and biological activity.

The term “fungi-based materials” includes several hyponyms: mycelium composites, mycelium-bound agricultural-fiber panels, fungal leather or mycelium-based textiles, molded packaging, insulation-like products, acoustic panels, and biofabricated coatings. These categories should not be treated as equivalent. A rigid panel made from sterilized substrate and post-cured at high temperature has a different indoor-air profile from a living or partially dried material used in a humid interior.

Mycelium composites: dried fungal networks bound to plant fibers

A mycelium composite is an engineered material in which fungal hyphae grow through a substrate such as hemp hurd, straw, sawdust, or other lignocellulosic fibers. The hyphae act as a biological binder. Researchers commonly stop growth through drying or heat treatment, after which the product may be compressed, molded, coated, or laminated.

Research summarized by Jones and colleagues in Materials & Design shows that density, substrate type, fungal species, cultivation conditions, and post-processing strongly affect strength, water absorption, fire behavior, and durability. These variables also matter for indoor air. A dense, dry, fully cured component is less likely to support further biological growth than a porous component that repeatedly absorbs water.

Living, uncured, and finished fungal products are different exposure categories

“Fungal material” does not necessarily mean “mold exposure,” but unfinished or inadequately dried products can contain residual spores, substrate dust, microbial fragments, or odor-producing compounds. Finished products may also release volatile organic compounds from the fungal metabolism, agricultural feedstock, adhesives, coatings, or packaging used during manufacture. The relevant question is therefore not whether fungi were involved in production, but whether the installed product is biologically stable and chemically characterized.

The U.S. Centers for Disease Control and Prevention states that mold grows where moisture is present and recommends controlling moisture to prevent indoor mold. This principle applies to mycelium products as it does to wood, paper, cellulose insulation, and other moisture-sensitive materials. A product marketed as “natural,” “compostable,” or “biodegradable” is not automatically suitable for a damp wall, basement, bathroom, or poorly ventilated enclosure.

Fungi-Based Materials May Reduce Some Chemical Burdens but Do Not Purify Indoor Air by Default

The strongest environmental case for mycelium materials concerns resource use and end-of-life options, not proven whole-building air purification. Mycelium can bind low-value agricultural residues into packaging, panels, and molded components, potentially replacing some petroleum-derived materials. However, sustainability and indoor-air performance are separate claims that require separate testing.

Volatile organic compounds require product-specific testing

Volatile organic compounds, or VOCs, are carbon-containing chemicals that evaporate into air at ordinary indoor temperatures. Some VOCs cause odor or irritation, while others may present longer-term health concerns depending on concentration and exposure duration. Fungal growth can generate microbial volatile organic compounds, but conventional finishing materials, coatings, binders, and contaminants in agricultural fibers can also contribute emissions.

There is no universal VOC value for all mycelium products. Emissions can change with curing temperature, humidity, age, surface area, packaging, and whether the product is coated. Buyers should request chamber-test results under recognized methods rather than rely on terms such as “non-toxic” or “chemical-free.” Relevant documentation may include California Department of Public Health Standard Method v1.2, GREENGUARD Gold certification, or another applicable low-emitting-material assessment.

Odor is a warning signal, not a complete health assessment

A mushroom-like, earthy, sour, or musty smell can indicate residual compounds, inadequate curing, moisture exposure, or microbial activity. Odor alone cannot establish whether a material is hazardous, because some harmful pollutants have little or no smell and some strong odors are irritating without being highly toxic. Nonetheless, persistent odor after installation warrants isolation, ventilation, and product investigation.

Adsorption claims should not be confused with air cleaning

Porous fungal composites may adsorb limited quantities of moisture or certain chemicals, but passive adsorption is not equivalent to removing pollutants at a controlled rate. Air purification requires known pollutant-removal capacity, airflow, contact time, regeneration behavior, and performance over the product’s service life. Unless those variables are measured, a mycelium panel should be treated as a furnishing or construction product—not as an air cleaner.

Moisture Control Determines Whether Fungi-Based Materials Remain Indoor-Air Neutral

Moisture is the critical bridge between a stable fungal composite and a potential indoor biological problem. Relative humidity, liquid-water leaks, condensation, vapor diffusion, and drying capacity can all affect performance. The World Health Organization’s indoor-air guidance identifies dampness and mold as important building-related health concerns, with associations reported for respiratory symptoms, asthma exacerbation, cough, and wheeze.

Humidity and water absorption are design constraints

Many mycelium composites are porous and can absorb water. Studies reviewed by Appels and other materials researchers report that moisture exposure can reduce mechanical performance and alter dimensional stability. A product’s laboratory density or dry-state strength therefore does not predict behavior after repeated wetting and drying.

The U.S. EPA commonly recommends keeping indoor relative humidity below 60 percent, ideally between 30 and 50 percent when practical, to reduce the likelihood of mold growth. These values are general building-health guidance rather than a universal product specification. Installers should also follow the manufacturer’s limits for temperature, humidity, liquid-water exposure, and vapor control.

Mold growth is usually a building-moisture failure, but materials can influence severity

If a roof leak, plumbing failure, flood, or condensation event wets a mycelium-based product, the product may become one of several nutrient-bearing surfaces in the assembly. The presence of a fungal manufacturing process does not make the material immune to other molds. Conversely, finding fungal DNA or spores does not by itself prove active growth or harmful exposure; visible growth, moisture measurements, odor, occupant symptoms, and professional inspection provide more useful context.

The practical rule is simple: keep the assembly dry, provide adequate ventilation, and repair leaks promptly. The EPA recommends drying wet materials within 24 to 48 hours when possible to reduce mold risk. Materials that cannot be thoroughly dried or cleaned after significant water damage may require removal.

Fungi-Based Materials Need Verification Before They Are Used in Occupied Interiors

A responsible specification combines life-cycle benefits with indoor-air, fire, moisture, and durability evidence. The absence of a strong odor or visible mold is not enough. A product intended for a bedroom, school, healthcare space, or office should have documentation appropriate to the risk and occupancy.

What manufacturers should disclose

• Fungal species or biological process used during manufacture.
• Substrate ingredients, recycled content, additives, binders, coatings, and preservatives.
• Moisture content at shipment and maximum permitted service humidity.
• VOC and aldehyde emissions measured in a recognized environmental chamber.
• Testing for mold resistance, water absorption, dimensional stability, and repeated wetting and drying.
• Fire classification, installation limitations, cleaning instructions, and end-of-life handling.

What specifiers and occupants should check

1. Confirm that the product is intended for interior use and for the proposed location.
2. Request third-party emissions data instead of relying only on marketing claims.
3. Inspect for musty odor, staining, softening, swelling, or visible growth before installation.
4. Control indoor humidity and address leaks before installing porous materials.
5. Use mechanical ventilation and source control; do not expect decorative panels to replace filtration or fresh-air systems.
6. If symptoms or persistent odor occur, remove occupants from the affected area temporarily and obtain an independent building or indoor-environment assessment.

Figure 1, recommended comparison chart: compare a sealed, fully cured mycelium panel, an uncured or damp fungal composite, conventional foam insulation, and a paper-based panel across VOC emissions, moisture sensitivity, mold risk, fire performance, and available third-party certifications. The chart should display measured values and test conditions rather than labels such as “natural” or “green.”

Conclusion: Fungi-Based Materials Require Evidence-Based Indoor-Air Claims

Fungi-based materials are a promising class of biofabricated products, particularly for replacing some fossil-intensive packaging and interior components. Their indoor-air effect is conditional, however. Mycelium composites can be stable and low-emitting when properly grown, dried, finished, tested, and protected from moisture, but they do not automatically purify air or prevent mold. VOC emissions, biological residues, water absorption, and the performance of coatings must be evaluated product by product.

The most important actions are to request emissions and moisture data, maintain indoor relative humidity around 30 to 50 percent when practical, repair water intrusion quickly, and treat unverified health claims cautiously. Further reading should include the U.S. EPA’s indoor-air and mold guidance, the World Health Organization’s dampness and mold publications, CDC building-moisture resources, and peer-reviewed reviews of mycelium-composite performance.

Sources: U.S. Environmental Protection Agency, “The Inside Story: A Guide to Indoor Air Quality,” https://www.epa.gov/indoor-air-quality-iaq/inside-story-guide-indoor-air-quality; U.S. Environmental Protection Agency, “Mold and Moisture,” https://www.epa.gov/mold; U.S. Environmental Protection Agency, “A Brief Guide to Mold, Moisture and Your Home,” https://www.epa.gov/mold/brief-guide-mold-moisture-and-your-home; World Health Organization, WHO Guidelines for Indoor Air Quality: Dampness and Mould, https://www.who.int/publications/i/item/9789289041683; Centers for Disease Control and Prevention, “Mold,” https://www.cdc.gov/mold/; Appels, F. V. W., Camere, S., Montalti, M., Karana, E., Jansen, K. M. B., Dijksterhuis, J., and Wösten, H. A. B., “Fabrication Factors Influencing Mechanical, Moisture-Related and Fire Properties of Mycelium-Based Composites,” Materials & Design, 2019, https://doi.org/10.1016/j.matdes.2019.108327; Jones, M., Bhat, T., Wang, C., Moinuddin, K., John, S., and Bååth, J. A., “Thermal Degradation and Fire Properties of Mycelium-Based Composites,” Fire and Materials, 2020, https://doi.org/10.1002/fam.2850; California Department of Public Health, Standard Method for the Testing and Evaluation of Volatile Organic Chemical Emissions from Indoor Sources Using Environmental Chambers, https://www.cdph.ca.gov/Programs/OLS/Pages/California-Volatile-Organic-Compound-Emissions-Standards-for-Indoor-Sources.aspx