Title Image

Producing mycelium insulation

Producing mycelium insulation

Interested in the power of mycelium?

Check out our new online course to learn more about this wonder material and make your own prototype!

After the theoretical research and the first experiments with mycelium, we got into larger production during the Summer School 2018. The first goal was start experimenting and eventually  produce mycelium insulation for the Summer School house. We prepared 27 panels (13m²) on the first week as part of the workshop given by Maurizio Montalti from Officina Corpuscoli and Mogu.


As a summary of the knowledge we developed during the Summer School, this article has two aims :

  • Submit a DIY (Do It Yourself) protocole to produce mycelium insulation panels, as we did with cardboard and wool insulation, measuring the technology’s costs, main disadvantages and benefits.
  • Define Critical Concrete’s own recipe to produce cheap, performant and ecological mycelium insulation through the bricks experiment.

Our work with mycelium is an ongoing process and we still have a lot to explore. Therefore we’ll conclude introducing the next steps to continue our research and production.


Panels production, materials





Spawn: Considering the non specialised environment in which we are working, Pleurotus Ostreatus (Oyster Mushroom) is the most performative strain to work with. It’s one of the easier mushroom to grow; it’s a strong mushroom able to compete with potential contamination. For these reason it’s perfect for anybody to work with in a non sterilized environment. In this case we are using 300 gr of Pleurotus Spawn to have the 7,5% of the weight of the wet substrate for each panel with dimension of 100x50x5cm.

Substrate: Since a few months we’ve been working with our friend Jorge Miguel Rocha Rodriguez, a mushroom farmer based in the surroundings of Porto. Thanks to him we had the opportunity to get a large amount of straw for a really good price, and get a first insight in the mycelium development process. His help was precious and if you’re ever thinking of developing this kind of technology, we invite you to find and contact local mushroom producers to accompany you in this adventure. This straw we used is a mix of different cereals which represents a rich substrate for mycelium. For each panel we were using 4 kg of wet straw.

Additives: To enrich the substrate we decided to add flour in the mixture. Flour contains sugar in the form of carbohydrates and is a way to stimulate the growth of the spawn and feed them. For each panel we decide to use a 10% of the weight of the wet substrate, 400 gr. In our last panels we added also corn wheat (s.a. Maïzena) in the same proportion.

Panels production, process



Pasteurization : Pasteurization is a method to reduce the number of bacterias in the substrate and the additives to give advantage to the development of spawn. To enable a faster colonisation and an easier handling of the substrate, we cut the straw in little pieces, 5/10 cm. Then we put it into boiled water with the flour; as the substrate the additive has to be pasteurize for 1h30.

Cleaning: After the pasteurization the environment in which we are working needs to be as clean as possible. We worked with reusable latex gloves, cleaning regularly our hands and all the surfaces in contact with the straw with alcohol, 70% minimum.

Cooling and squeezing: The growth of the spawn requires special conditions in terms of temperature and humidity: the ideal temperature is between 20°C and 25°C (25°C being the optimal one). Highest temperature can kill the spawn and drive the growth of other type bacterias that can damage the other spores; lower temperature won’t enable the spawn to grow. In terms of air humidity, the ideal percentage is around 65%.

These requirements induce two steps: the straw has to cool down and has to be squeezed until no more water is flowing out before the inoculation. We take the straw out of the pot with sterilized spoons, spread it over a clean surface and squeeze it, before keeping it into cleaned and closed boxes to protect it. This passage is really important in order to regulate the quantity of water and humidity inside the moulds and to avoid too much condensation in the panels. This part of the process is open air: it means the straw is in contact with a lot of bacterias even if all the surfaces in contact with it are cleaned with alcohol. Faster this part is done, better it is.

Inoculation: After cleaning the mould with alcohol, we mix the straw creating different layers. We put half of the straw and half of the quantity of spawn, mix it, then the other half of the straw and spawn, mixing it again. To have stronger and more dense panels we press the straw paying attention to the corners and possible holes with lack of material. Then the mould needs to be sealed but drilled with several little holes, made with a needle, to enable spawn to breath. During its growth the spawn needs oxygen and releases CO2. In this way spawns are growing in up direction to reach the the O2.

Growing period: As we said, our conditions are not ideals to grow mycelium. When it takes one to two weeks to have a panel ready to dry in lab conditions, it took us more than one month. During this period, panels were closed in the dark, exposed to temperature varying between 20°C and 28°C during the day, falling between 15 and 20°C during the night. Humidity depends also on the squeezing quality and the variations of the weather. A good solution it’s to check these variables with a thermometer and cover the moulds with blankets if you need to increase the temperature. Mycelium panel is a real ecosystem and the place for the struggle of different microorganisms. We observed the development of four different Fungi as Pleurotus Ostreatus, Trichoderma, Aspergillus and Chrysonilia sitophila and the birth of some midges. Every different types of fungi are fighting with the others in order to win and eat the substarte reach of favority food for Fungi: cellulose. For that reason, whether it is in lab conditions or not, the growing period needs to be supervised. In this time you have to wait and just observe the fight between bacterias, molds and fungi; also in case of a strong contamination, your mycelium can anyway fight foreign bacterias. During these phase the mycelium is strong and very fast to growht. As a normal kind of vegetable live they start, very soon, to produce their own fruit: mushrooms. In order to avoid these growht and to have the same density of mycelium in any directions you can flip the panels different times.

Drying: At one point, the panel is entirely colonised by the spawn and a thick white skin has grown homogeneously around and inside it. The development of this skin is quite important for the rigidity and density of the panel. At this point, the panel needs to be dried to eliminate as much as possible the humidity that can facilitate later the growth of unwanted microorganisms and of your own spawn. We dry the panel three days on a roof exposed to the sun with a temperature varying between 18°C and 28°C. Just pay attention to left the panels not in contact with edible materials from mushrooms as wood, cardbard and other material with natural origin, because they can encourage the regrowht of mycelium spawn.

Ending: As we work on insulation panels, we need to work with a lifeless and stable product. This means we have to kill the spawn to end its growth. If we were just drying the panel, a humid environment could activate again the growth of the spawn inside the panel and outside on the surfaces in contact with. As we said, the spawn can’t outlive high temperature; beyond 80°C the spawn can’t survive. Thanks to our previous reseraches about rocket stoves we construct an outdoor rocket oven to heat the panel at this temperature during 1h. The time of bake depends on the thinckness of the panel; our panels are 5 cm thick.

Finishing: As we said the mycelium insulation has very good capacity and quality, but it suffers the contact with humidity. For that reason it’s better avoid the position in rooms as kitchens and bathrooms.  After drying and baking the panels they are a stable material; so a choice can be to left the surface without finishing in order to appreciate the texture of this material, that depends from the type of substrate and mushroom that you used. If you don’t like the texture of this material another possibility can be close it a sandwich wall with wood panels, or paint the surface with natural and transpiring painting.

Pictures from the workshop given by Maurizio Montalti (Summer School 2018): pasteurization, cooling, squeezing, mixing, growing, heating.

Rocket oven: materials and drawings.

Workforce and time

Preparation: As part of the workshop given by Maurizio Montalti we prepared 27 panels in 3 days with a group of 10/13 students. Even if this workshop was punctuated by theoretical interventions and explanations about the process, this time can hardly be reduced. Indeed the preparation of the panels depends on the pasteurization time and is limited by the volume of the pots.

Growing period: This time is variable. In our conditions it can take between 10 days to more than 1 month. The process can take longer if the substrate is too humid, if the environment of the room is not well controlled or if the equipment is not well cleaned during the preparation. It can also depend on the quality of the spawn.

Panels evolution from day 1 to day 21: the mycellium of Pleurotus Ostreatus is growing and fighting against other bacterias and moulds.

Ending: The drying time represents around 3 days, but it’s also depending on the weather. Then the heating represents 1h per panel, meaning 3 days more to heat the 27 panels in relation to the quantity of panels that you can bake in just one time.

When working with living material, it’s hard to define a precise estimation of the time needed to produce panels. Based on our experience we can imagine producing 15 panels meaning 7,5m² in a minimum of 19 days in optimistic conditions. Then this approximation is subject to variations.

Panels production, problems and benefits


Main disadvantages

Contamination: Working with living organism means we can’t fully control all the process. Whether it is in a laboratory or in a non-specialised environment, there will always be a margin of error resulting from the quality of the spawn and the possible contamination by other microorganisms.

Time scheduleBesides the risk of contamination, our conditions of work make us dependent on natural factors as the weather that will affect the moisture content and the temperature, two important datas to optimize the growth of the spawn and the drying time. This means that we’ll always have to plan extra time in the schedule of the production and we’ll be dependent on the seasons. However our research on ecological heating system is a way to face this point.

Plastic: Growing mycelium requires rigour on cleanliness of the space and the material. Metal and plastic were the two materials we had that could be easily cleaned with alcohol during the Summer School. We used a lot of cellophane that means a lack of other material solution. In the laboratories that are working on mycelium, the use of plastic is current. Our goal is to avoid it as much as possible to provide truly ecological products. At least we now replace the cellophane with a more durable plastic cover that can be reused virtually indefinitely.

Long run: As the research on mycelium is still fresh, we don’t have the necessary hindsight to evaluate its sustainability in the long run.



Mycelium properties: Different studies already showed the fire resistance and thermal properties of mycelium. Mycelium insulation panel doesn’t need any treatments against fire and can be as competitive as classic insulation in terms of performance.

Low-cost and energy process: As we’re working with an organism which is growing by its own in conditions we can provide, mycelium production is a way to benefit from natural energy and work with limited resources. As a natural material growing without artificial energy it’s sustainable during all life cycle.

Introduce a new aesthetic: Social and ecological architecture is an opening door to innovation throughout the research. With mycelium we really see the possibility of developing a new aesthetic that could raise awareness about nature and its range of possibilities.

Growing mushrooms: During its growth, the spawn produces edible mushroom. Mycelium panels are more than an insulation solution, they represent a temporary food production.

Bricks experiment


The aim of this experiment is to improve our knowledge about mycelium and its properties, trying to define Critical Concrete’s own recipe to produce cheap, performantive and ecological insulation panels. Improving the process also means to be able to produce by our self another type of insulation and, as we already did with cardboard, to produce and to put in work this material.

To this end we decided to produce 19 bricks respecting the same proportions of substrate, spawn and additives, but experimenting different mixtures each time.


Follow-up schedule of the bricks experiment

Spawn: Pleurotus Ostreatus (Oyster Mushroom)

Substrates: We compared different substrates (straw, cotton, cardboard, sawdust, cork, coffee ground and line fibber) using the materials we already had in Co-Lateral. We focused on the most accessibles for us (cheap and locals), meaning cardboard, straw and cork (local and not cheap :)).

Additives: Adding complements enrich the substrate to optimize the growth of the spawn. They have different roles : supply deficient nutrients, correct the pH of the substrate, keep a good humidity and aeration. We used calcium and gypsum to correct the pH ; grape seed, maïzena, sugar and cat food to supply and improve deficient nutrients.


Pictures of the 19 bricks on the august 15

On the 8th/9th day (depending on the brick) of the growing period a clear difference already appears: some bricks develop faster than others.

Photos order from brick 1 to 19.



The results of this experiment are really encouraging for us: the most appropriate substrate for our spawn seems to be cardboard. In terms of additives, maïzena is the most competitive, followed by sugar and the mix calcium/gypsum. Still have to wait for the performance tests of the bricks.

Overall costs calculation


For the Summer School 2018 we planned a budget to produce 22,5m² of insulation that means 45 panels of 100x50x5cm. It represents a significant cost (772,27€) that has to be divided in two parts: the equipment investment and the material cost.

Equipment investment: The main part of the mycelium budget was dedicated to this investment (600,63€); the moulds being the most expensive part, half of it. Once this material is bought it’s reusable and long lasting. Therefore, for the next years this cost will be significantly reduced (53,54€ is an optimistic forecast for the Summer School 2019).

Ingredients cost: Even if we had the opportunity to get a large amount of straw and mycelium for a good price, thanks to Jorge Miguel Rocha Rodrigues, we know we can reduce this cost. We have to work on partnerships with supermarket and companies as Lipor to collect their cardboard and use it as a substrate instead of straw. The material costs will be reduced and the process will be more performing, as the bricks experiment showed us. Regarding the spawn cost, we already did some experiments with Miguel to produce Mother Spawn. These experiments were positives and gave us the knowledge to make our own spawn. We are now working on the construction of a laminar box to become completely independent on that point. Therefore, the budget of the material will be reduce to the price of the source material to produce spawn.

Summer School 2018, budget for 45 panels (22,5m²)


Equipment Price per unit, kilo and litre Quantity Total costs
Pots 40x40cm 53 €/un 2 106,00 €
Propane gas bottle 25,50 €/un 1 25,50 €
Gas cooker 92,25 €/un 1 92,25 €
Plexiglasse mould (100x50x5cm) 21 €/un 15 315,00 €
Recycled plastic boxes 45L 5 €/un 6 30,00 €
Natural latex gloves 0,69 €/un 20 13,80 €
Alcohol 70% 3,56 €/lt 4 14,24 €
Cellophane (30m) 0,64 €/un 6 3,84 €
600,63 €


Ingredients Price per unit kilo Quantity Total costs
Straw 0,43 €/kg 151 kg 65 €
Spawn (Pleurotus Ostreatus) / / 94,64 €
Flour 0,4 €/kg 30 kg 12 €
171,64 €
Budget for 22,5m² 772,27 €

Summer School 2019, budget for 45 panels (22,5m²)


Equipment Price per unit, kilo and litre Quantity Total costs
Propane gas bottle 25,50 €/un 1 un 25,50 €
Natural latex gloves 0,69 €/un 20 un 13,80 €
Alcohol 70% 3,56 €/lt 4lt 14,24 €
53,54 €


Ingredients Price per unit kilo Quantity Total costs
Cardboard 0 €/kg 150 kg 0,00 €
Spelt 2,49  €/kg 22,5 kg 56,03 €
Calcium carbonate / 0,0225 kg /
Gesso 0,2 €/kg 0,0450 kg 0,01 €
56,03 €
Budget for 22,5m² 109,57 €

Mycelium on the marketThe estimation for the next Summer School is optimistic but considers the main costs of the production. Compared to the market prices, mycelium seems to be a sustainable solution to produce cheap and ecological insulation. The Summer School 2018 confirmed us the interest of this material in social and sustainable architecture.

Market prices, budget for 22,5m²

Types of insulation Price per square meters Quantity Total costs
Glass wool 11,16 €/m² 22,5 m² 251,10 €
Rock wool 13,01 €/m² 22,5 m² 292,73 €
Wood wool 18,04 €/m² 22,5 m² 405,90 €
Hemp wool 17,45 €/m² 22,5 m² 325,13 €
Sheep’s wool 33,90 €/m² 22,5 m² 762,75 €
Expanded cork 49,89 €/m² 22,5 m² 1122,53 €
Expanded Polystyrene insulation (EPS) 19,58 €/m² 22,5 m² 440,53 €
Extruded polystyrene insulation (XPS) 24,81 €/m² 22,5 m² 558,23 €
Polyurethane 34,95 €/m² 22,5 m² 786,38 €




The Summer School 2018 was a real opportunity to improve our knowledge about mycelium. It confirmed us the interest of this material in social and sustainable architecture and gave us the next guidelines to continue our research. We sincerely want to thank Jorge Miguel Rocha Rodrigues and Maurizio Montalti for all their input and their contribution in this project.

Now the next steps for us are as follows:

  • testing our bricks prototypes and decide our own recipe, using recycled substrates
  • becoming independent in all the process; from mother spawn production with a laminar flow hood
  • improve our process, avoiding the use of plastic as much as possible
  • controlling the environment of the mycelium room in terms of light, temperature and humidity
  • continuing the experiments to keep developing our method better and better


See you for the next publications – about our successful full sized cardboard mycelium panel!

Liked it? Take a second to support our reseach on Patreon!
Become a patron at Patreon!