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Out of the Box – Insulation

Out of the Box – Insulation

Layers of cardboard

One of our carboard panel prototype

Cardboard represents one of the largest component of municipal solid waste around the world. This material, often associated with the very basic sheltering for homeless thanks to its unlimited availability, can be re-used as an affordable insulating solution for impoverished people suffering from heat-leaking households.

With expanding the reach of global shipping industry connected with rapidly escalated e-commerce in the last decades, the packaging materials such as cardboard or bubble plastic wrap, among others, glut the landfills worldwide immensely. Common use of “russian doll” method of product packaging requires tons of new material that has to be effectively recycled.

According to Laurie L.Dove’s research, making cardboard products out of recycled ones takes 25% less energy and creates fewer greenhouse-gas emissions than production of new cardboard (1). However, after five to seven recycling loops, the fibers become too short to bond together into cardboard. In this case, adding new pulp during the recycling process, usable fibers can still be transformed into more fine product such as paper.

Diagram of different cardboard types
Various types of cardboard products by Ecobox recycle company, image: www.ecobox.my

In Portugal, according to the Urban Waste 2014 report, published on the Portuguese Environment Agency’s (APA) website, Portugal’s overall performance in terms of recycling was 29 percent, while the target is to reach 50 percent in 2020 (2). This scenario requires a significant investment in recycling infrastructure, however, without changing people’s dumping habits the goal will not be accomplished easily.

Another solution to get rid of excess waste is its re-use. That can result both in upcycling – giving the waste another life and downcycling – degradation of identity and quality of the original material. In compare with the traditional way of recycling by sorting and chopping up the material into little pieces, upcycling requires much less added energy for processing and transport of the waste-material. From the creative point of view, upcycling triggers new applications in the building-industry and gives birth to the variety of unexpected designs.

In the case of void-filled corrugated cardboard, it possesses many features that are desirable in a building material such as light-weightness, stiffness and thermal insulation.

One of the pioneers in experimentation with cardboard insulation and its structural qualities in buildings is American educational institution Rural Studio based in Alabama, which used bales of wax-impregnated corrugated clippings for the construction of a house in 2001. Mixed with cement, the cardboard bales were used for foundation and floorings as well (3).

Cardboard Pod
Corrugated Cardboard Pod project by Rural Studio (2001)

Critical Concrete tackles two concerns in one action by reusing left-over cardboard, while helping energetically poor families in Portugal to insulate their houses. The collective starts prototyping alternative insulating panels in the framework of its Research Lab’s agenda. Using cardboards as insulation should take advantage from cellulose thermal qualities in combination with simple low-tech manufacture, affordability and very good ecological balance (less embodied energy, less toxicity than fiberglass and other furnace-produced mineral insulation).

The main technical challenges that have to be resolved in order to secure safe use of cardboard insulation are inflammability, mold and insect infestation. Borax or boric acid could be used to increase the resistance of the panels to smouldering and flaming combustion, and simultaneously works as a contact poison for insect. The toxicity of borax is questionable, but it is recommended to seek installation methods that minimize dust. We chose to treat the insulation by a wet application process, immersing or spraying the cardboard, and sample different proportion of borax until 20% of the weight of cellulose insulation.

Borax crystals from Kramer, California, USA, image: Natural History Museum, London.

Other challenges that have to be faced are the water absorptivity and the mold, especially in Porto where the most of our interventions on socially relevant spaces take place. Humidity combined with deficient ventilation causes most of the degradation of the house, which can not be fixed by insulation solely. However, the treatment with borax should also answer this problem, but this point should be tested very carefully during our technical test. Due to these deficiencies, the cardboard insulation is more suitable to use on those attics, walls, crawl spaces, etc., that will remain dry.

The team also conducted a series of investigations on the tools of production. We needed to find a way to assemble cardboards together, either by a binder agent (plaster, glue) or with a physical process, and then to make it dry. Thus the collective starts prototyping a box with the objective to produce it in large quantities. Therefore the box to mold the insulation panels has to guarantee a production flow.

One of the boxes we made as a base for our prototypes.

After several attempts with the first box prototype a few problems became clear to us. The panels needed too much time to get dry, missed dimensional accuracy and the box had to be cleaned after every panel. So for the modified version we use a grid instead of plywood for cover and bottom to permit a fast drying. Furthermore, we integrate a stopper to guarantee the same thickness of every panel and cover the plywood parts of the box with foil to keep them clean. Ready for next attempts…


[1] Dove, L.L. (2017)“Has Online Shopping Changed How Much Cardboard We Use?”. HowStuffWorks. [Online] available at: https://science.howstuffworks.com/environmental/green-science/online-shopping-cardboard-consumption-industry-amazon.htm.

[2] The Portugal News (2016).Portugal still way off 2020 recycling goals”. [Online] available at: http://www.theportugalnews.com/news/portugal-still-way-off-2020-recycling-goals/38280.

[3] Rural Studio (2001). “Corrugated Cardboard Pod”. [Online] available at: http://www.ruralstudio.org/projects/corrugated-cardboard-pod.

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