Welcome to Filaments! I’m Silvia Hüttner, and this is a limited-run newsletter which tells the stories of how fungi have been, are and will be changing the world. You’re getting it because you signed up at buttondown.email/filaments and you can unsubscribe at any time with the link at the bottom of this email.
In the last episode we discussed eating filamentous fungi, in this episode we will look into the possibilities of wearing fungi, building with fungi and even being buried in fungi.
As far back as the Neolithic, people cut the mushroom Fomes fomentarius off tree stumps and transformed it into the felt-like material Amadou to make hats and vests. Also called tinder mushroom, it was also a popular flammable substance and even Ötzi the Iceman had some of it in his pockets when he was crossing the Alps.
Amadou was for a long time the only fungi-based material in common use, but this is about to change. In the last ten years, materials made with or from fungi have started to pop up in design and art magazines, as chairs, lampshades or wallets or even as whole buildings. So far mostly used as concept pieces or promotional material from design studies, fungi products might finally go mainstream in 2021. The New York Times wrote about fungi being “fall’s hottest fashion trend” and Adidas very recently announced the development of “a new material, a purely biological leather alternative made from mycelium” that they will use “for the very first time in the creation of footwear”. It’s not that often that people get excited about fungi on their feet.
So let’s look into what kind of fungi materials there are, how to make them, and why they’re exciting. We’ll start with leather.
“There are traditionally two ways to make a leather jacket. One involves a cow, and takes years. Another involves synthetic fabric, and requires plastic. But there’s a third option: thick sheets of woven fungus, grown over a couple of weeks on anything from sawdust to agricultural waste.” (Source)
Remember how mycoprotein is made in big vats for food, as described in Episode 2? You can make fungal leather in much the same way - where the fibrous mycelium pulp is pressed into sheets like paper pulp in traditional paper-making.
More commonly though, fungal leather is obtained by solid state fermentation, meaning that the mycelium grows in mats on a bed of nutritious solid particles, often agricultural waste, such as straw or sawdust. This is less energy-intensive than liquid cultivation, and also allows the mycelium to grow in its naturally self-assembling, three-dimensional structure, which is important for the texture and durability of the resulting material.
Pressed and dried mycelium mats (Credit: Bolt Threads)
Some species are more suitable than others . The fungi used for this process are usually of the mushroom-forming variety (basidiomycetes), therefore the growth conditions have to be adjusted carefully to suppress mushroom formation and get only the desired dense mats of mycelium. Indonesia-based Mycotech - who launched fungi sneakers and wallets in 2019 - experimented first with the common oyster mushroom, before switching to Ganoderma (also called Lingzhi or Reishi) because it gave better results. Generally, polypores - which you can often find on the side of tree trunks - are used for creating fungi materials, because they grow in a denser structure than other fungal species.
After 5-10 days of growth, the mat of interwoven mycelium is harvested, pressed and dried to obtain a material that is already surprisingly leather-like. It doesn’t need a full-on tanning process like animal leather, though some chemical treatment is necessary to make it more resilient and improve its properties. Soaking in glycerol increases elasticity and strength  and immersing in acid or alcohol removes undesired soluble components and results in crosslinking, which gives the material additional strength and durability. Bleaching or treatment to eliminate odour might also be necessary. After that, the fungal material is pressed and dried, and dyed or imprinted if desired. The result is a material with a nice organic texture, velvety and soft to the touch, a bit like stroking a dry camembert.
Despite not being a completely chemical-free process, production of fungal leather has a much lower environmental impact than animal leather or conventional synthetic leather, which is made from petroleum-based PVC. A big advantage is also that the mycelium mats can be grown to sizes of several square metres and to many desired shapes or thicknesses.
Being a biological growth process, no direct energy input is needed (if grown in solid state fermentation and at ambient temperature). And since the species of fungi used are wood degraders, the growth substrates are typically waste or by-products from forestry and agriculture, or even paper and cardboard, which makes the production process in essence an upcycling process.
Considerable energy input is however necessary not only for the steps after growth (such as pressing and drying), but also for sterilising the raw materials before the fungi can grow on them. This is usually done with heat and steam, but there are less energy-intensive alternatives such as submerging the raw material in peroxide solution for an hour, or in cold water for a few days.
Perhaps surprisingly for a new technology, cost estimates show that mycelium leather is cheaper to produce than comparable animal or synthetic leather varieties , since the raw materials cost next to nothing.
Mycelium leather samples (Credit: Bolt Threads)
So what are the difficulties in making fungi leather? In an environment where the raw material is literally agricultural waste teeming with thousands of organisms, contamination is one of the biggest issues manufacturers are facing. Even with rigorous sterilisation and cleaning procedures, it’s tricky to avoid other microbes growing alongside the desired fungus, possibly resulting in a damaged product or no product at all.
Another issue is inconsistency. Biological processes can be finicky, and fungal growth is no exception. Changes in temperature, humidity, substrate composition, time of day, light, CO2 concentration, etc. lead to variations in growth, resulting in products with inconsistent thickness, texture, colour or structure. And customers tend to like consistency.
Fungal leather hasn’t been on the market very long yet, so longer-term durability is still unknown. And one of the biggest selling points of fungal leather is also up for discussion: its biodegradability. While pure mycelium can be completely biologically degraded within weeks, polymer composites or coated mycelium materials might not be (and take as long to decompose as the least-biodegradable component in the mix). If fungal leather is mixed too much with other materials, we might end up with the same problem that coated paper and bioplastics face, which is that they are hard or impossible to recycle properly once they reach the end of their life or use.
Mycowork’s Reishi (which was presented at NY fashion week in February 2020), for example, incorporates polyester as reinforcement and has a polylactic acid coating, which gives it higher tear strength and higher flexibility than even animal leather, but also makes the material hardly biodegradable.
“In theory, we can grow Reishi in any shape, whether that’s something very large and seamless, or smaller custom shapes that eliminate all the waste associated with cutting a hide. With leather, you’re essentially cutting arbitrary patterns into a cow-shaped hide and so a lot of our brand partners are excited by the fact that Reishi can be grown in any shape–both for the design possibilities that creates and the reduction of waste.” (Matt Scullin, Mycoworks CEO, Source)
Mycoworks was founded in 2013 by Sophia Wang and Philip Ross, an artist that has been working with mycelium since the 1990s. The other prominent player in the field is Ecovative, a mycelium materials pioneer that was founded in New York in 2007. Ecovative partnered with Bolt Threads - a biomaterials company also making artificial spider silk by yeast fermentation - to bring the product Mylo to the market (though not without legal problems along the way). Mylo debuted in April 2018, and partnerships with Adidas, Lululemon and Stella McCartney promise fungi-based garments in stores in 2021.
There are still only a handful of companies developing fungi leather, and most of them have very similar ideas about naming their product: Mylo (Bolt Threads), Mylea (Mycotech), Mylium (Mylium), MycoFlex (Ecovative), Pura Flex (MOGU), and Reishi (Mycoworks).
Getting your hands on some fungi lederhosen will still take some time though, as most of these companies don’t yet have large scale production. Instead they’re looking for funding (some through Kickstarter) or have entered exploratory collaborations with designers (as mentioned above).
But things could change quickly, especially if existing mushroom farms are adapted to become the leather producers of the near future. Already Mylo is being grown in European warehouses that used to produce mushrooms for the gourmet market.
Fungal mycelium growing in stacked trays (Credit: Bolt Threads)
Leather is the most fashionable, but certainly not the only material that can be made out of mycelium. Fill some sawdust into a container, add the right kind of fungi spores, wait a few days, and you get a compact block of a natural mycelium composite that is dense, light and surprisingly strong. The mycelium acts like a glue binding the particles together (while also partially digesting them). After baking and killing the living fungi, the material is dry and durable.
Mycelium bricks stacked on top of each other (Credit: Mycoworks)
If “blocks of light, dense material” remind you of polystyrene, you’re not alone. Several companies have explored the possibilities of making fungi-based packaging to cushion expensive wine bottles or computer parts. Ecovative (with the brand Mushroom Packaging) licenses its technology of how to grow mycelium in moulds to get the exact right shape and size to snugly hold a product in place. Companies in New Zealand, the Netherlands, the USA and the UK use Ecovative’s technology to offer custom-made packaging solutions, including one made of hemp and mycelium that Lush uses to ship soap.
However, packaging is literally made to be thrown away once you’ve removed the actual product, and so it needs to be a very low-cost product. It’s hard to imagine mycelium foam to be more than a gimmick for high-priced products, since there is already a cheap, widely used, environmentally-friendly solution widely available: paper and cardboard.
On the other hand, however, fungi-based packaging can be directly made at the farms that produce the primary raw materials, and could offer a more local and low-emission packaging solution that doesn’t require cutting down trees . If that’s enough to compete with existing materials, or if fungi packaging will remain an ultra-niche product, remains to be seen.
Nevertheless, fungi’s unique ability to fill and grow into any shape can be used to make more than just throw-away packaging. Italian-based MOGU uses agricultural residues to develop fungi floor tiles and acoustic panels, while Ecovative has made lampshades and other interior products from mycelium, and has (together with Ford) explored the use of fungi foams in car doors and car seats. Conveniently, mycelium composites have been found to absorb noise very well, especially the range of car noise (1,000 Hz) and are more fire-resistant and release less smoke than plastic alternatives .
Lampshades made out of mycelium (Credit: Ecovative)
Fungi can even be used to construct buildings. The construction sector is a major contributor to greenhouse gas emissions, and materials that can be regenerated offer a path to reduce those emissions. Dr. Jan Wurm, director of the international architecture and construction firm Arup, says that “we need to use materials that are grown, that are biofabricated”.
Fungi to the rescue! Mycelium blocks can be used as cheap and fire-resistant construction and insulation material. Not only are these materials biodegradable, but they can also trap more heat than fiberglass insulation, are fireproof, nontoxic, and stronger than concrete relative to its weight .
There are some downsides, of course. Low water resistance can be a problem in construction use, making the material vulnerable to humidity and - ironically - mould. Mycelium material in stable conditions has a lifespan of decades, but when in contact with wet ground it can start decomposing in a matter of weeks. In that sense, mycelium behaves like untreated softwood. Like wood, the mycelium bricks can be treated with coatings that make them more resilient but might compromise the 100% biodegradability factor. It’s a thorny problem to solve.
“The future of materials is going to be grown – biofabricated – and mycelium and its extraordinary ability to assemble itself into complex structures is what will enable us to take biofabrication to the next level of performance.” (Eben Bayer, Ecovative CEO, Source)
Nonetheless, there are already buildings in the world made of fungi. The first large-scale structure made from mycelium bricks was the MoMA PS1 Young Architect’s Program’s winning entry “Hy-Fi” in 2014 which was built with material from Ecovative. After the exhibition, the bricks were composted and used as fertiliser.
The "Hy-Fi" structure made out of mycelium bricks (Credit: The Living New York)
Going a step further, the architecture studio Redhouse has designed a whole mushroom-based ecosystem. The studio’s “BioHAB” runs as a pilot project in Namibia: an invasive plant species is harvested to be used as a growth substrate for mushrooms that can then be eaten and sold. The leftover mycelium bricks from the mushroom farm are subsequently used to build houses. Redhouse has also developed the Biocycler, a machine that grinds cellulose-containing construction waste, then re-binds the pieces with fungi and calcite-producing microbes into a new durable material, which is then processed into blocks.
Another project exploring the possibilities of fungal architecture is the FUNGAR project, which not only experiments with building structures out of mycelium, but also integrating living fungi into construction. (More about that in an upcoming episode!)
Some more niche applications of fungal material are found in mortuaries. Many fungi are saprobes - or “eaters of the dead”. Artist Jae Rhim Lee took this literally and designed a burial suit that is infused with mushroom spores and mycelium, which can speed up decomposition and help break down the over 200 toxic chemicals that are found in a human body. For the complete fungi burial experience, Loop of Life offers a coffin made entirely out of mycelium (with technology licensed from Ecovative).
Other emerging applications of fungal material are in the field of biomedical engineering and cell cultivation. The cells used in tissue engineering and lab-grown meat production need a scaffold to grow on. This can be provided by the intricate network of mycelium, which is both compatible with cell growth and edible. Additionally, sheets made from mycelium have been shown to improve wound healing  and could find applications in medicine.
As early as in the 1950s, patents have been granted for including fungi in the papermaking process to improve fire resistance of paper. Newer studies describe nanopaper containing mycelium compounds with uses as specialised membranes, filters and packaging .
It doesn’t stop there. Other applications for mycelium materials include sound absorbers and ear plugs, biodegradable floating wetland panels for habitat creation and shoreline protection , and rigid mycelium films that can become a replacement for the widely-used plastic high-density polyethylene (HDPE) .
Acoustic wall panels from MOGU (Credit: Luca Alessandrini)
In short, there’s still a lot of room for innovation and research when it comes to growing the products of tomorrow. The input influences the outcome; fungi cultivated on one substrate (such as wheat straw) look and feel different than fungi grown on another substrate (such as sawdust). Even sawdust from different kinds of trees can give varying results.
Different fungal species can also have vastly different characteristics when it comes to mechanical properties, looks and material behaviour . Getting consistent products at large-scale will be the biggest challenge for mycelium material producers.
The technology to manufacture fungal materials, especially at a large scale, is still in development. Ecovative first grew mycelium in open trays, but later invented a system where growth takes place in a solid-state bioreactor which supplies air at the right humidity and temperature to the fungi. Currently though, mycelium cultivation is still done mostly manually, without much automation . And, ironically, a lot of plastic is used to make the fungal material, since mycelium bricks are often grown in single-use plastic bags and moulds.
Finding the right customers is another challenge. A lot of the applications of fungal material are in low-price segments, such as packaging or insulation. That’s why at least initially most companies in the area target art galleries, design studios or organisations that want a few expensive statement pieces. To make fungi-based materials affordable for the mass market, economies of scale are needed.
Having said that, we will certainly also see more fungi furniture, design products and clothes in the future, made by small studios and artisans. The manufacturing process of, for example, mycelium leather is much more accessible than traditional leather making. Growing products our of fungi could become a new craft where artists, small businesses but also commercial mushroom cultivators experiment and develop new ways of using mycelium.
 Fungi as source for bio-based materials: A patent review. Cerimi et al., 2019. https://doi.org/10.1186/s40694-019-0080-y
 Fungal mycelium classified in different material families based on glycerol treatment. Appels et al., 2020. https://doi.org/10.1038/s42003-020-1064-4
 Leather-like material biofabrication using fungi. Jones et al., 2020. https://doi.org/10.1038/s41893-020-00606-1
 Mushroom packages. An Ecovative approach in packaging industry. Kim & Ruedy, 2019. https://doi.org/10.1007/978-3-319-53121-2_27-1
 Waste‐derived low‐cost mycelium composite construction materials with improved fire safety. Jones et al., 2018. https://doi.org/10.1002/fam.2637
 Physico-mechanical and thermodynamic properties of mycelium-based biocomposites: A review. Girometta et al., 2019. https://doi.org/10.3390/su11010281
 Fungal mycelia as the source of chitin and polysaccharides and their applications as skin substitutes. Su et al., 1997. https://doi.org/10.1016/S0142-9612(97)00048-3
 Nanomaterials derived from fungal sources - Is it the new hype? Nawawi et al., 2020. https://doi.org/10.1021/acs.biomac.9b01141
 Advanced materials from fungal mycelium: Fabrication and tuning of physical properties. Haneef et al., 2017. https://doi.org/10.1038/srep41292
Thank you for subscribing to this limited run newsletter about the fascinating things fungi can do and how we can use them. My name is Silvia Hüttner, I’m a biotechnology PhD, fungi enthusiast and a researcher specialised in fermentation and enzyme technology. I’d love to hear from you if you have any questions, comments or suggestions, or just want to say hi. Just hit reply. 🍄
Finally, thanks also to Antoni Gandia, R&D Specialist at MOGU and former Research Scientist at Ecovative, for interesting conversations that helped me dig into this rapidly-expanding field.