Deep Dive: Mycelium
What is Mycelium?
A mushroom is often the first thing people think of when they hear “fungus.” However, the mushroom is just the fruiting body of a fungus. There are many more stages of life hidden from the human eye. Before forming a mushroom, a fungus grows from a singular reproductive cell called a spore into hyphae, cells that form tendrils and secrete enzymes to break food into nutrients that the fungus absorbs. As the hyphae grow and branch, they form a web-like mass called mycelium. Mycelium sprouts mushrooms, which then produce spores, which allow the fungal life cycle to begin again.
For materials, mycelium is the most important part of the fungal life cycle. Emerging materials use mycelium to create anything from vegan leather and bacon to insulation and bricks to packaging as an alternative to foam.
I used grow-it-yourself kits from Grow.bio by Ecovative. In these kits, the branching structure of mycelium binds loose, wood-chip-like substrates together to create solid forms. The substrate in the panels in Material World is hemp hurd, a byproduct of hemp processing. The mycelium panels are naturally water-repelling, flame-resistant, and acoustically insulating. They can be composted in a backyard setting in as few as forty-five days. Full material information for grow-it-yourself kits can be found here on Grow.bio’s website.
Mycelium Growth: Process
In order to create the molds for the mycelium, I needed to finalize the exhibit walls in Rhino so that the panels I made fit the final exhibit. I used many of Rhino’s analysis tools, particularly to estimate the volume of mycelium needed and the lengths of curves. To determine the height and width dimensions of my molds, I relied on information provided by my Grow.bio saying that “The material will shrink 4% in the X and Y, and 7% in the Z direction” when dried. With this, I calculated how much larger the molds needed to be to counteract the shrinkage, and built the final molds to fit these dimensions.
The above notes are how I kept track of calculations for the size of my plywood molds and the volume of mycelium I anticipated needing.
Since I wanted the mycelium panels to match the curve of the exhibit, I extracted curve profiles for the ribs of the molds directly from the exhibit rendering in Rhino. Combined with data on how much the panels would shrink once dried, I used this information to develop vector drawings of ribs for the back and front of the mold. I then used these drawings to cut the ribs out of ½” plywood on the CNC machine. The ribs for each panel were attached together with strips of plywood stapled on each end.
I developed Rhino cut files for the ribs and bases of the plywood molds, and nested them in a square the size of the piece of plywood I had available.
A rough sketch of the mycelium growth molds. Not to scale.
Then, I stapled ¼” plywood along the edges of the ribs to make solid surface for the mycelium to grow against. I drilled holes in an inch square grid to allow mycelium to breathe, and then coated all the pieces in a water-based polyurethane so that the mycelium wouldn’t grow into the molds. Had I not covered my plywood molds in polyurethane, I would not have been able to remove the mycelium from them since it would have grown into the porous woodgrain. It should be noted that although the water-based polyurethane provided a layer of protection necessary for my molds, it does contain plastic.
Each panel for the mycelium molds is laid out to dry after a primary coat of water-based polyurethane.
After the polyurethane cured, I drilled holes through the sides and bottom of each mold to attach the side and base panels that held the assembly together, creating a container closed on all sides but the top, where I could pour mycelium into the mold.
The mold on the left has side walls bolted to the curved panels. The mold on the right is clamped together so that I can drill holes for bolts.
Before packing the molds, I built a 3’x3’x6’ structure out of 2x4s that was then covered in plastic sheeting in order to create a somewhat controlled growth environment. To grow mycelium, you need to create a growing environment that is as sterile as possible. The mycelium feeds on flour, but flour also serves as a food source for bacteria and mold. Thus, enclosures help to keep contamination at a minimum. Any tools used to handle mycelium and molds in which the mycelium will grow need to be sanitized with rubbing alcohol. I also wore rubber gloves that I rinsed with rubbing alcohol before handling the mycelium. Trying to keep mycelium sterile generates a good amount of waste that might never be seen if only the final product is shown.
3’x3’x6’ wood structure, nicknamed Mike Celium, sheathed in plastic to create a sterile growth environment.
Once I mixed my mycelium with flour, I started filling the molds. Between pours, I packed the mycelium down. My theory was that the more tightly packed the hemp hurd substrate was, the stronger and more rigid the panels would be. However, because of the packing, each mold used more mycelium than expected. The product data said each ten pound bag of mycelium contained one cubic foot, and my calculations indicated that the volume of seven panels would equal just under two cubic feet. Thus, I thought I would get three to four panels out of one bag of mycelium. Ultimately, though, I used one and a half bags to make just two mycelium panels. Later, I needed to order another shipment of mycelium to make my seven panels. Doing so increased my carbon footprint, as the living material is shipped with UPS Next Day Air shipping.
Above: My brother helps me pack a mold with mycelium.
Left: Mycelium mixed with flour sits ready to be packed into sanitized molds.
Once packed, I sealed the molds on the exposed top with plastic wrap and tape, after which I placed them into the growth chamber. There, they sat for five to seven days to let the mycelium grow, binding the hemp substrate into a solid mass.
Fully packed mycelium molds were covered in plastic and left to grow.
At the end of the growth period, I unscrewed the molds, took off the sides, and then carefully peeled the mycelium away from the curved mold surfaces, to which the mycelium was suctioned. At this point, the mycelium was damp and dense. The panel as a whole almost felt rubbery.
Refilling the empty molds involved sanitizing them with rubbing alcohol, bolting the pieces back together, and packing them yet again to restart the growth cycle. I completed this process four times.
Left: Mycelium molds with the side panels removed after six days of growth.
Right: A mycelium panel freed from one of the curved mold panels.
When the panels were freed from the mold, I placed them in a homemade oven of reflective bubble foil insulation with a space heater at one end. This process kills the mycelium and stops its growth so that the product stays stable. Each panel I grew remained in the oven for three to four days, during which the space heater ran for about eight hours a day. I don’t know the exact amount of energy consumed by a space heater for hours every day, but I can imagine it creates a significant carbon output. This, in particular, is a part of the process that could generate negative environmental impacts if the electricity powering the heat source is generated from fossil fuels. In a large-scale growth setting, one could, perhaps, run ovens off of a renewable energy source, thus minimizing the carbon footprint of the desiccation of the mycelium.
For safety reasons, I do NOT recommend running a space heater for long periods of time in a set up like this.
My makeshift oven had a hole in the front of the insulating bubble foil box for the space heater, and holes on each end for ventilation.
After I finished growing and drying all the panels, I tested three different finishes. In the end, I sealed them with a soft wax made out of beeswax and carnauba wax.
The finished panels are lightweight, like foam.
The mycelium panel in the upper right corner has three finish tests. From top to bottom: PolyWhey, wax, hemp oil. The wax finish changes the appearance of the mycelium least visibly.
Evaluating Sustainability
Although not visible in the final panels, the process of growing the mycelium involved significant use of plastic, specifically plastic sheeting, cling wrap, and reflective bubble foil insulation. Additionally, although I don’t have a number on the amount of energy used, I imagine that running a space heater all day for several days has a negative impact.
Although mycelium is an exciting material that has the potential to replace unsustainable materials such as styrofoam, I believe that it is most environmentally friendly when grown at an industrial scale, especially if they have systems in place to create reliably sanitary spaces and desiccate the material using heat generated from renewable sources. These industrial settings still have the potential to generate large amounts of waste as a production byproduct, even though mycelium itself is fully compostable. At the scale I was working in, I am not sure that the plastic waste from production and carbon footprint generated by shipping the material and heat drying the panels was offset completely by the environmental benefits of the mycelium. Still, though, it is difficult, if not impossible, to exactly quantify this cost versus benefit. Does the educational impact have the potential to offset my small-scale waste? These are some of the difficult questions that often come into play when trying to work towards sustainability.