Building with fungi

Over the past two decades, scientists have experimented with growing mycelia – the networks of hair-like threads that sustain all fungi – to create new materials. And our mycelial appetite is mushrooming, with startups the world over securing millions in funding for their low-carbon, biodegradable (and sometimes edible) products. Now, scientists and engineers are turning to mycelia to help shape the buildings around us.

While mycelium is no replacement for concrete or steel, it does have potential for internal and non-load-bearing materials, from stud walls to doors and insulation. Since many construction materials are derived from petroleum, mycelium could be a good alternative.

Some companies and researchers are taking the concept even further, with early prototypes of temporary buildings made from mycelium bricks. Others propose living mycelial structures that can grow and shift with time. But what many mycelia-material proponents have in common is a belief in the need for a mentality shift in the way we construct and experience the buildings around us.

Flexible fungi

Unlike photosynthesising plants, fungi get energy from digesting organic matter such as cellulose and lignin. They can convert this into mycelium and fruiting bodies, such as mushrooms. Depending on the type of fungi, the medium they grow in, the CO₂ content, temperature, and air humidity, mycelium can form materials with completely different qualities: rigid, foam-like, flexible, dense, loose, strong, or easily torn.

For example, mycelium can be grown as a ‘skin’ or layer on the surface of a liquid containing starch, sugars, yeasts, and other nutrients. Fermenting solid substrates is another approach to grow mycelium materials. Vegan leather grown this way by US-based Bolt Threads has already been used in Stella McCartney bags and Lululemon yoga mats. Mycelium vegan meat, which can resemble steak or bacon, involves a similar approach.

Mycelium can also grow in a dry layer of agricultural by-products, such as shredded corn husks, sawdust or straw. As the fungi part-digest the plant matter, they bind the remaining waste fibres in a rigid but lightweight composite structure. This can result in a material akin to polystyrene that can be used as packaging. In the UK, The Magical Mushroom Company has produced and sold over half a million pieces of packaging made this way, using an approach developed by US-based Ecovative. After use, mycelium packaging can be torn into smaller pieces and composted with garden waste, turning to soil in about 45 days.

Building with mycelium

While mycelium-based construction materials are still a nascent area, enough progress has been made for many a headline speculating about compostable future homes made of living fungus. But these are not wholly unfounded ideas.

The materials and foresight teams at Arup have been researching biomaterials such as mycelium in the built environment for over a decade. Back in 2014, they provided structural engineering for an eye-catching temporary structure made from mycelium composite bricks. This art exhibit, the Hy-Fi Tower, was installed in a courtyard at New York’s Museum of Modern Art (MoMA).

Arup’s engineers worked closely with New York-based architecture practice The Living to come up with a design. After testing the composite material’s strength, they calculated that the bricks (made using Ecovative’s approach) could be used in a structure up to 12 metres high. Aiming for a structure capable of withstanding 65 mph winds, their design featured a wide base and round towers.

This striking project numbers in the few that have used mycelium for external, load-bearing bricks. “There are still significant barriers for mycelium, including technical understanding, particularly in terms of longevity in exposed environments and structural applications,” says Florence Wu, a biomaterials specialist on the Arup team who has been involved in several recent mycelium-based projects, including an award-winning initiative to restore wetlands with floating mycelium islands.

Wu also worked on acoustic insulation tiles, conceived by Italian company Mogu. Mogu’s foam-like, sound-absorbing tiles are designed to reduce noise and echo in internal spaces such as offices. The company worked with Arup to determine the product’s technical specifications.

“In nature, fungi are formidable decomposers and recyclers, responsible for transforming dead organic matter,” explains Mogu’s co-founder, designer and engineer Maurizio Montalti.

“In our case, they hold the potential to process low-value materials, such as agro-industrial waste, and turn those into high-value materials and products.”

Growing the data on mycelium

Testing was an integral part of product development. Mogu worked closely with the Arup team for this, gathering data on sound absorption, fire safety, compressive strength, humidity resistance, and performance after installation.

“We often had to go back to the drawing board when the result wasn’t in the accepted range or couldn’t be reproduced,” says Montalti. “There were many iterations. We shared the data with Arup, to… eventually [establish] a process that would consistently deliver a high-performing product.”

“We assessed and analysed their data in relation to building standards,” adds Wu. “Having robust testing and data that shows performance and compliance is crucial to gain the trust of the public, to inform engineers and builders, and enable policymakers to legislate, paving the way for wider adoption.”

Despite the consumer appetite for materials with a lower environmental impact, as Wu points out, lack of data is a major barrier to biomaterials being more widely adopted. For instance, many mycelium products have limited data on durability. And without evidence that they fulfil specifications – either stipulated by building regulations, or performance required by a client – they are unlikely be used.

There is more manufacturers and researchers working with mycelium must do to better understand and tailor its properties. For instance, the amount of water it absorbs is important for indoor use, especially in humid climates. One mycelium expert has compared it to a sponge, noting it should be sealed with water repellent (which could compromise its sustainability credentials). Others report that mycelium composites, densely grown on the right substrate, have more suitable water absorption properties than clay bricks, mortar and glass fibre.

Either way, more R&D and case studies will clarify what is possible. The Living’s latest project will test mycelium as insulation, sandwiched between millimetre-thick sheets of a fibreglass shell, for the walls of prefab affordable housing units in California.

Cost is also an obstacle, with many mycelium products considered high end and niche. If projects such as The Living’s are successful, they could raise mycelium’s profile and in turn, demand for it, bringing down prices.

Living buildings

Dr Meng Zhang, an associate professor in microbial biotechnology at the University of Northumbria, believes that mycelium products can go even further in construction – but depends on close collaboration between engineers, architects and biologists. She says this cross-pollination is critical if these emerging biomaterials are to fulfil their potential.

“R&D goes hand-in-hand with large production processes,” she explains. “[Understanding] the biology of mycelia is essential. Engineers and scientists… must continuously monitor substrates and growing conditions.”

Working to capitalise on such partnerships, Dr Zhang and her colleagues secured £8 million in funding from Research England to establish the world’s first Hub for Biotechnology in the Built Environment. This initiative from the universities of Newcastle and Northumbria involves bioscientists, architects, designers, anthropologists, and engineers. The hub envisions a future in which living buildings reduce pollution, metabolise their own waste, and generate energy.

Dr Elise Elsacker, a former group member who is now a research fellow at the Vrije Universiteit Brussel, has demonstrated results to this effect. Her work shows that with the appropriate treatment, mycelia can regrow after goods have been created. “That would enable products that could regenerate, such as self-healing leather. For example, if you have a cut in the leather surface, you could add a nutrient that regrows the broken leather,” says Dr Zhang.

While self-healing mycelium leather is in its early stage, Dr Jane Scott, a textile designer, and her colleagues at the hub, grew mycelium onto a wool, paper waste and sawdust matrix to form an arched, cave-like structure for the launch of the University of Newcastle’s Farrell Centre for architecture and cities in April. The mycelium can be regrown if cracks appear, while the entire structure is compostable at end of life.

The Living Construction group is also exploring how mycelium insulation could be grown in cavity walls, and ‘welding’ materials with long mycelium filaments as an alternative to cement. While at a very early stage, this would have vast potential, given that 5% of global CO2 emissions stem from the cement industry.

Montalti, too, sees promise in bio-fabrication – the ability to use cultured organisms to “create technical products that specifically address a need sustainably,” he says. “Fungi can, for example, produce chitin within their cell walls, the same hard material making up the exoskeleton of shrimps.”

Dr Zhang believes that mycelium products could fundamentally change the construction industry and be an important step towards a circular economy. “Living materials hold huge potential to construct in a new way. Living cells could transform how we build.”

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This article has been adapted from "Building with fungi", which originally appeared in the print edition of Ingenia 95 (June 2023).