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Mycelium Cardboard Insulation

Mycelium Cardboard Insulation

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After the good results from our mycelium experimentations during the Summer School 2018 we decided to explore further the promising results from the cardboard bricks to improve our production process. This new step in our research was lead by the objectives of reducing the economical costs and the time of the production for a future bigger scale production.

Final results of cardboard brick experiments made during Summer School 2018.

A comparison of experiences:
straw vs cardboard

The experience of the Summer School 2018 was a good opportunity to understand the potential of cardboard and start thinking further in its possibilities of use. Looking in this direction and highlighted by our previous research, we compared the cardboard with straw, another material that we already used.

The principal characteristics that an insulation material needs are thermal, acoustic, fire and water resistance and steam. In order to make a proper comparison in a sustainable production perspective, it’s also important to think about other characteristics related to the two materials such as their specific weight, nature, composition, production process as well as costs.

Note:  the table sums up the comparison between cardboard (left) and straw (right) characteristics.
* Borax is a good treatment to make cardboard fireproof. Exact fire class unknown.
Source: Materials prices mined from local market.
** Depending on application mode. Source: Straw fire class reference

After analysis, the cardboard emerged as a real competitive material to work with; both for its technical performances and for its nature, composition and costs. Cardboard is a lightweight, free and recyclable material that is suitable for a sustainable construction. Regarding its insulation properties, cardboard has poor thermal conductivity which makes it a great insulation material. In addition, this material turned out to be a good substrate for growing mycelium and mushrooms thanks to its cellulose composition (90%), the favourite mushrooms’ “food”.

New methodology and recipe

The cardboard brick experiments and results made during Summer School 2018 oriented us in the selection of a better recipe and technique of production. From the two options tested, the first one made from superposition of cardboard sheets layers, gave a poorer result in the mycelium growth. The little size of the Pleurotus Ostreatus mycelium spawns (3-4 micron) are not able to break the cardboard fibers and to grow up fast enough. The final result is a brick with a very hard and compact skin that is not really colonized in the internal part. Therefore, using a substrate composed by little pieces of cardboard seems a better option, giving the opportunity to the spawns to sneak freely into the substrate.

From the bricks experimentations, we followed and improved our methodology of the straw panel production to make the cardboard one. The substrate is made with pasteurized cardboard; pieces of 15×15 cm are boiled for 1,5 hour in hot water; and additives; in our case, corn flour (maïzena for example).

To avoid any type of contaminations from external bacteria, the corn flour is previously pasteurized in glass jars placed in a pressure pot and cooked with two cycles of 30 minutes each.

This process mixes better the substrate and the additives than putting directly the additives to the substrate in the water during the pasteurization. In every molds we put the wet substrate with less than 10% of its weight in additives same as spawns: 11 kg of wet cardboard, 800g of corn flour and 1,1kg of Pleurotus Ostreatus spawn. Because of its cellulose composition, the cardboard requires less quantities of additives than with straw; 10% instead of 20%; while giving a competitive time of growth.

To produce the cardboard mycelium panel, we used 100x50x5cm plexiglass molds. A perforated cover with little holes; a needle thickness size placed in a grid of 5×5 cm; allows the oxygenation of the panels and the mycelium to grow. The 5cm thickness of the panel could be used in a combination of different insulation layers (same or different materials) to have complementary results in the insulation production.

Evolution of the cardboard panel in 3 months: from inoculating phase until baking.
Final panel after baking

Test and results

The technical properties of this new insulation panel technology will be soon verified with our newest local collaborator, the ITEcons from the University of Coimbra. Thanks to this opportunity we will be able to compare the results with our prototypes about thermal conductivity, acoustic performances and fire resistant. Until this time we started to make some basic tests and experimentations to control the reaction of this material to fire and water.


The panel is really solid and compact, but it’s easy to cut just with the help of a cutter or a fine saw. The texture inside is really fine, dense and fully colonised by the mycelium spawn.

Fire test

The fire test was done through putting the prototype in direct contact with the flame of a candle for three times: the first time for 1 minutes, the second for 2 minutes and the last one for 3 minutes. We were able to note that the mycelium skin is not completely burnt and protects the cardboard from contact with the flame.


The last experiment was made to test waterproof properties: as we discovered, flowing water on the surface is not a factor of damage for the material. Above we can observe the drops not penetrating the surface.


Using cardboard as a substrate reduces the cost of the production and offers the possibility to start a more competitive production. In this perspective and to improve the whole process, reducing the time to realize the panels goes along with the time consumption efficiency of the different phases. In this process, the first step, cutting cardboard, seems the main issue which could easily be improved by using a box cutter.

After the experience of Summer School 2018, the production costs have been sensibly reduced.

For each panel of 0.5 m2, we are using now 11 kg of free wet substrate, 800 gr of corn flour (1,98€) and 1,1 kg of mycelium Pleurotus Ostreatus spawn (5,83€). The global material cost for the production of one panel is 7,81€; representing in the end 15,62€ for 1 m2. Of course these costs can be optimised when you get corn flour in big scale and are able to reproduce mycelium yourself – see the laminar box below. This result represents half of our initial production cost during Summer School 2018 and becomes a more competitive product for the ongoing market when compared to the straw mycelium panels.

Tabs prices resume.
The €/m² price for cardboard mycelium panels is mined from our current experience.
The €/m² price for straw mycelium panels is mined from the work during the Summer School 2018.
Types of insulation


Glass wool 11.16
Rock wool 13.01
Wood wool 18.04
Hemp wool 17.45
Sheep’s wool 33.9
Expanded cork 49.89
Expanded Polystyrene insulation (EPS) 19.58
Extruded polystyrene insulation (XPS) 24.81
Polyurethane 34.95

Complete the cycle:
from laminar flow hood to production center

Production cycle of mycelium panels.

On our exciting path of mycelium research and growth, we looked on a way to close autonomously the whole cycle of the production. To improve further our methodology we produced a serie of tools and instruments needed to complete the different phases of the process: a laminar flow hood for spawn reproduction and growing, a rocket stove to bake and produce, a moving production center to be able to fabricate autonomously in a bigger scale.

The laminar flow hood, a space for spawn reproduction

For making the production process even more autonomous and further lower the costs, we can replicate the mother spawn of myceliumin a sterilized environment, instead of buying the inoculated seeds.

Thanks again to the help of our friend Jorge Miguel Rocha Rodriguez from Congumelos do Migaas we decided to build a laminar flow cabinet.

A laminar flow cabinet is a carefully enclosed bench designed to prevent contamination of biological samples or any particle sensitive materials. The air is drawn through an HEPA filter and blows in a very smooth, laminar flow towards the user. A laminar flow cabinets may have a UV-C germicidal lamp to sterilize the interior and its content for 15 minutes before usage to prevent the contamination of the experiment. This instrument will allow us to replicate mycelium in different phases.

Laminar flow diagram
Laminar flow cabinet

Laminar flow hood: materials 

The first step is the replication of the mother spawn from one petri dish to another one by dividing the content from one to the other. Then, to reproduce the spawn, you put the spawn from the petri dish into different jars previously filled with pasteurized wheat grain as “way of transport” of the spawn. The grain is previously pasteurized in jars in a pressure pot for two cycles of 30 minutes each.

The laminar box in itself is built with a wood structure, an internal cover in inox steel or wood painted with washable paint (to allow an easy and sure cleaning of the surfaces on which to work on) as well as an external one built with wood. The slopes’ front part is realized with two plexiglass parts: one openable and one fixed. Our box measure 90x60x60 cm and has a section shape of a trapeze. This design gives some comfort in the use of the box, but different options and choices can be experimented. The most important aspect to consider is the choice of the fan and the filter that have to be carefully related to the dimension of the box, instead of the quantity of air present inside it.

The rocket oven

Working on insulation panels requires to work with a lifeless and stable material to avoid the over-growth and lifelong of the mycelium and the potential damages that they could cause when installed on site. Unable to live over a high temperature, a baked panel beyond 80°C will have no risk of further growth once in contact with a humid environment.  

To conduct this baking panels process we have already constructed and experimented an outdoor rocket oven during Summer School 2018.

The design of the rocket oven is really simple and easy to assemble and disassemble in any different time. It’s basically composed by two walls made with brick and a G shape chimney in the middle. In the upper part, five metal “L profiles” allow to create a support for a grid and the cooking area. The correct temperature of 80° is provided for both surfaces of the panel thanks to two inox metal sheets that create a closed environment with a relatively internal uniform temperature.

We baked the panels, 5 cm thick, at this temperature during 1h, 30 minutes for each sides.

A nomad production center

Having in the same place all the tools and the materials to grow mycelium spawns and panels could definitely improve the production cycle and allow us to fabricate autonomously on a bigger scale.

Design a nomad, moving production center from site to site, thought as a container of tools and experiences seems already to be one of our next challenges!

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