Wool on the Wall

Our latest research has been focusing in alternative methods of insulation and how these can be applied in an old building and serve as efficiently as other popular ways of insulation. We have already wrote about the properties of cardboard (see here) and how it can be used as an insulation material. In this article we will introduce you to our research about sheep wool, made possible thanks to our partnership with Burel, who provided us with a bunch of wool leftovers for our tests. Expect in the near future more articles about our research on cardboard, as well as a sneak peak on the mycelium investigation.

Sheep wool (along with other animal origin materials) was used by prehistoric communities to make clothes or insulate their huts and houses. Many centuries later, in 15th century, the sheep wool was used by the british to make clothes, when in 20th century, sheep wool insulation emerged on the market. Wool has incredible insulation properties as it can efficiently protect the sheeps in very harsh conditions. Furthermore consists a 100% natural and sustainable insulation product, as it is — obviously — naturally produced and it can be disposed without causing any environmental impacts at the end of its life. Wool can effectively absorb moisture and release it back to the air as heat. A proof of that is that when we empty the washing machine, the only clothes that are completely dry are the ones made of wool.

Nevertheless, natural wool not only has the potential to protect sheep from cold and humidity, but it can also protect them in dry and hot conditions. This can be achieved due to wools’ fibers that create air pockets and can trap the air, exactly the same form that corrugated cardboard provides[1]. This ability allows wool to absorb and then release moisture from/to the air, without compromising its thermal efficiency. So when the wool absorbs the moisture, it generates an amount of heat which allows it to stabilize the heat changes that are caused by humidity. Additionally to its thermal insulation properties, wool can also serve as an acoustic insulator and has also the ability to clean the air from serious gases such as formaldehyde[2].

Image 1 Sheep wool life-cycle, image source: http://www.sheepwoolinsulation.ie/why_wool/

While searching the insulation properties of wool, it seems like a promising material considering its efficiency and sustainability. However, we should seek the possible ways that we can obtain it and the processing that it is needed in order to install it. Unfortunately, wool cannot be found so easily and in such large amounts as cardboard. Nevertheless, the woolen cutoffs of clothes companies that are normally disposed, can efficiently meet our demands. Fortunately, these samples are already treated and can be placed immediately on the construction site, in contrast with raw wool which needs to be treated in order to reach its properties and maintain its durability. The commercial wool insulation can be found either in the form of batts or rolls that have specific dimensions, or in loose-fill fiber form (image 2) which can fit in any application. Both forms though contain clean and treated wool in order to make it insect resistant and fire retardant.

Image 2 Loose-fill fiber wool insulation, image source: https://thedaedalusproject.wordpress.com/2013/05/

In order to explain the techniques of cleaning and treating the raw wool, we should understand its substances which make it so resistant and appropriate for insulation. Sheep produce two main ingredients from their skin which are absorbed by wool, grease and sweat. Lanolin, is the grease/oil produced by the sheep’s skin and suint is similar to sweat. Cleaning technique of wool aims to remove both lanolin and suint, in order to facilitate the processing of the wool and prevent it from moths, mainly because both lanolin and suint attract them. On the other hand, some people state that the removal of lanolin is not necessary, because it consists the main substance of the wool that repels water.

Generally, the cleaning process of wool aims at the removal of three things: the lanolin, the suint and the dirt. There are several different ways to clean and wash the wool, but in our case, we will study those that can be accomplished without specialized machines. At first we have to pick the fibers of wool by hand, or by beating the pieces of raw wool with sticks, like we do when we want to remove the dust from a carpet. This procedure will remove most of the dust that is stuck inside the wool. Then we should proceed with the washing which can be done in several ways at home: by washing with soap which removes the dirt and the suint but not the lanolin, by putting the wool into the water and allow it to soak until most of the sticky paste is removed, or by washing it in the (front)washing machine which will remove dirt, suint and lanolin completely.

When the cleaning of the wool is finished and the wool is dry, we should treat it with borax[3] in order to make it repellent to insects and reinforce its fire retardant properties. This can be achieved by dissolving the borax in hot water and spray it on the wool. Then the dry wool should be carded either by carding machine or by hand using large brushes. When the carding is done, the wool should be fluffy and smooth with air spaces between the fibres. The phase of carding is very important as it provides the wool with its greater thermal and acoustic insulation properties.

The last phase of wool treatment contains its modification into panels. The process can be accomplished by attaching lines of wood on kraft paper by using adhesive material. Thus, we can have wool insulation batts which can be installed on the walls easily as panels.

Despite its advantages, wool insulation develops also some difficulties which we should examine in order to find the best situations in which we can possibly use it. To begin with, sheep wool it can be expensive to buy, comparing to other types of insulation. According to Chris Magwood and Jen Feigin[4], the production of raw sheep wool is limited or sometimes the product must be transferred from one area to another, which results in high costs. But, the most critical disadvantage of wool is its vulnerability to insects and especially moths. Before installing the insulation we should guarantee its resilience in moths and insects, which can be accomplished by treating it with borax as mentioned above. Additionally, another feature that defines a good insulation material is if it is fire retardant. In this case the situation is more complicated as when the wool comes to contact with fire it reacts as hair. So it doesn’t actually burning but it is charring and thus prevents the expansion of the fire. With the addition of borax, we guarantee the repulsion of insects while we endure wools’ fire retardant properties. Last but not least, we should mention that the life span of wool, as any other materials’, cannot be calculated as it depends on several factors as weather conditions, treatment etc., but in case of wool, the major problem is its protection from the insects. If the treatment has been done properly, then the wool can last for up to 50 to 60 years without losing its insulation properties.

Considering all these information about how we can use wool as an insulation material, we started the construction of a prototype panel made from shred pieces of woolen clothes. Burel, a Portuguese company working with local materials, producing amazing clothes, carpets, scarfs, and all kind of textiles products with wool, offered us their leftovers.

Image 3 Detail from our first wool insulation panel

To begin with, our prototype was based on the idea that the wool insulation will be installed on a construction site, responding to the context we often face in our workshops. Thus, we decided to take advantage of the beam structure of the walls and install the wool insulation inside without creating extra panels. This solution was optimized by our decision to cover the wool insulation with recycled windows, another abundant resource[5], in order to make the (colorful) insulation visible and protect it from the dust, simultaneously. Although the wool insulation can be installed in the whole surface of the walls, we suggest this transparent construction for upper parts, where the glass is not exposed to mechanical impacts. Now we will describe the process of the insulation installation step by step. It is important to say that we made the prototype as a frame using the same beams that it will be used in a wall construction.

1st step:

Dissolve borax powder into boiled water (20 teaspoons/1l water)[6] and spray or apply with a brush on the woolen pieces in order to protect them from insects. Usually the clothes pieces are already treated, so the borax solution is optional.

2nd step:

Prepare the window by removing the useless parts such as handles, hinges etc.

Steps 1 and 2

3rd step — optional:

Prepare the construction site by putting a fence between the beams, to create a back for the wool insulation.

4th step:

Screw the first window[7] and start filling the gap with wool from above, until the surface behind the window is covered. Then continue the process until the area you want to insulate is covered.

Steps 3 and 4

The installation of the woolen insulation can be accomplished also on the ceiling, but in this case we should find a lighter way to cover the wool, than the windows, such as thin plywood for example. The next step of our research will be the testing of the properties of the wool insulation. Stay tuned to figure out if our wool insulation is resistant to fire and humidity, see our next prototypes, or if different types of insulation can be combined and serve our cause!

In text references:

[1] Corrugated cardboard can serve as an excellent insulation material thanks to the holes that are formed inside it, it has the potential to trap the air and deter its exhaustion.

[2] Bosiaa, D., Savioa, L., Thiebata, F., Patruccob, A., Fantuccic, S., Piccablottoa, G. & Marinoa, D. (2015). “Sheep wool for sustainable architecture”6th International Building Physics Conference, IBPC 2015.

[3] Borax / Boric acid differences: Borax is a mineral known for its antifungal, antimicrobial and antiseptic effects. Generally is not a dangerous mineral, it is often used as a pharmaceutical or cosmetic product. Borax is often confused with boric acid but they are not the same: borax is alkaline not an acid. Boric acid is the chemical bond of borax with hydrochloric acid or other kind of acid, and it is often used as a fertilizer.

[4] Magwood, C. & Feigin, J. (2014). Making Better Buildings: A Comparative Guide to Sustainable Construction for Homeowners and Contractors. Paperback publications, 2014.

[5] This is an efficient way to use the unused windows and doors that can be found in large amounts in the construction sites.

[6] This proportion of borax/water results to 10% dissolution. It is important to be careful and not inhale the dust created by the borax powder!

[7] Before placing the windows in position, it is better to cover the beams with woolen pieces in order to prevent the thermal bridge, as good as possible.


[1] GreenHomeBuilding (n.d.).“Natural Insulation”. [Online] available at: http://www.greenhomebuilding.com/QandA/materials/insulation.htm.

[2] Appropedia (n.d.).Natural wool insulation”. [Online] available at:http://www.appropedia.org/Natural_wool_insulation.

[3] Bozsaky, D. (2010). “The historical development of thermal insulation materials”, Periodica Polytechnica Architecture, 41(2), pp. 49-56. DOI: https://doi.org/10.3311/pp.ar.2010-2.02.

[4] McCrea, A. (2011). Insulating your house: A DIY guide. Crowood Press.

[5] Natural Wool Insulation (n.d.). Natural Wool Insulation Do it yourself”. [Online] available at:http://naturalwool-insulation.com/natural-wool-insulation-do-it-yourself/.

[6] The Green Age (2017).The advantages of sheep wool insulation”. [Online] available at:https://www.thegreenage.co.uk/advantages-sheep-wool-insulation/.

[7] Ecologic Construction (n.d.).“Sheep Wool Insulation”. [Online] available at: https://ecologicconstruction.com/category/3-products/wool-insulation/.

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