What Is Sheep’s Wool Insulation (Why Should We Use It)?

A photograph of a worker handling bundles of sheep's wool insulation in the factory, next to a second photo of a lamb in a field. Across the top of the image are the words, "What Is Sheep's Wool Insulation (Why Should We Use It)?"

Image on left courtesy of Havelock Wool.

We often think of traditional materials like foam and fiberglass when insulating our homes and buildings. But have you ever thought of using sheep’s wool?

Yes, you read that right – sheep’s wool insulation can be used to insulate your home, and it’s use is gaining popularity due to its sustainable and renewable nature.

However, the question remains, “What is sheep’s wool insulation, and why should we use it?

Sheep’s wool insulation is a natural insulation made from sheep wool. This insulation is often treated with borax to make it more fire-resistant. Besides being sustainable, sheep’s wool insulation has an excellent R-value of 3.5 to 3.8 per inch, making it an excellent thermal insulator.

In the rest of this article, I’ll discuss how sheep’s wool insulation is used for building and its benefits.

Moreover, I’ll compare it with other insulation materials in terms of cost to help you make an informed decision. Let’s get started!

The Renewable and Sustainable Nature of Sheep’s Wool Insulation

A photograph of a flock of sheep standing close together next to a second photo of a sheep's fleece that has been newly sheared. Overlain in the middle of the image a two green circular arrows to indicate renewability and sustainability.
Sheep’s wool insulation is a renewable building material because wool naturally replenishes itself when it grows back each year.

Sheep’s wool insulation is both sustainable and renewable.

Although sustainable and renewable materials are terms that are often used interchangeably, they are not the same thing.

Let’s remind ourselves of the distinction between sustainable and renewable materials to understand why sheep’s wool insulation is both sustainable and renewable.

A renewable material is made with natural resources that natural processes can replenish or replace quickly. Sheep’s wool insulation meets this criterion because sheep produce wool through an ongoing natural growth and shedding process.

The process is repeated over and over again without harming the animal. That’s why a single sheep provides about 4.5 kg of wool annually.

On the other hand, a sustainable material is one that’s renewable and meets further specific criteria related to its environmental, social, and economic impact throughout its lifecycle.

In a nutshell, a sustainable material must meet the following conditions:

  • It is produced and used in a way that minimizes its adverse effects on the environment.
  • It promotes social and economic development.
  • It is produced and consumed without depleting natural resources.

Sheep’s wool insulation meets the above sustainability conditions because:

  • It uses natural resources that are replenished by the sheep themselves.
  • Its production process doesn’t involve pollutants or hazardous chemicals.
  • It’s biodegradable and safe for disposal with minimal environmental impact.
  • It helps create jobs in rural areas and boosts the economy.

How Is Sheep Wool Used for Building?

A house roof viewed from inside during construction with sheep's wool insulation fitted between the timbers.
Sheep’s wool can be place between wood members of a roof to provide excellent R-values. Image courtesy of Havelock Wool.

Sheep wool is used for building as a concrete reinforcement agent, insulation, soundproofing, and carbon fiber precursor.

Let’s dive into the different ways sheep’s wool is used in building for a clear understanding.

Sheep’s Wool as a Concrete Reinforcement Agent

Unlike conventional concrete, fiber-reinforced concrete uses fiber reinforcements like glass, carbon, and polypropylene.

Adding these fibers to concrete improves its:

  • Compressive strength
  • Tensile strength
  • Crushing strength
  • Abrasion resistance
  • Toughness

Unfortunately, many of the different fibers used to reinforce concrete are unsustainable. For instance, polypropylene has been the main fiber used for concrete reinforcement. However, manufacturing propylene requires hydrocarbons which, in turn, generate massive amounts of carbon dioxide.

Consequently, replacing polypropylene concrete reinforcement with sheep’s wool, a natural fiber, became desirable.

According to Science Direct, using sheep wool fiber in concrete increases its compressive, tensile, and flexural strength. The table below shows the results obtained with seven concrete specimens:

SpecimenCompressive Strength After 7 Days (N/mm2)Compressive Strength After 14 Days (N/mm2)Compressive Strength After 28 Days (N/mm2)

Table 1: Compressive strengths of sheep wool fiber reinforced concrete. Source. Science Direct

Sheep’s Wool for Insulation

A sheep's fleece with a cartoon outline of a house overlain. The house has an icon inside to indicate heat and cold, which looks like half a sun and half a snowflake combined.
Sheep’s wool is an excellent thermal insulator, which has evolved over millennia to keep sheep warm in the winter. It can also be used very successfully to insulate buildings and reduce heating and cooling costs.

Although insulating a house helps save an average of 11 percent on total energy costs, the efficiency depends on the type of insulating material.

The efficiency of an insulating material depends on its thermal conductivity, density, and R-value.

Before proceeding, it’s worth clarifying the difference between two measures commonly used to describe the insulating properties of different materials – thermal conductivity and R-value.

Simply put, thermal resistivity (R-value) is the inverse of thermal conductivity (U-value). Therefore, higher R-values indicate better insulation, while lower U-values indicate better insulation.

Sheep’s wool is used in construction for insulation due to its high thermal conductivity and low thermal resistivity per unit area and thickness.

With a low thermal conductivity rating of 0.038 to 0.040 W/mK, sheep’s wool offers excellent resistance to heat flow. In fact, wool provides more heat flow resistance than mineral wool, with a thermal conductivity of 0.044 W/mK.

Moreover, sheep’s wool has a higher R-value of up to 3.8 per inch. Therefore, it’s an ideal insulator even in very cold climates.

Sheep’s Wool for Soundproofing

Sheep's wool sound insulation panels mounted on a wall. They are rectangular and brown.
Sheep’s wool sound insulation panels are very effective at keeping noise out of a listening room and minimizing echoes. Image courtesy of Havelock Wool.

Wool features interwoven fibers with micro diameters and thin walls, which form millions of air chambers. These properties enhance wool’s acoustic insulation, making it an excellent sound absorber.

According to a study by the National Library of Medicine, sheep’s wool exhibited high sound absorption coefficients at mid and high frequencies, making it ideal for sound absorption.

With an average Noise Reduction Coefficient (NRC) rating of 0.75, sheep’s wool is an excellent choice for soundproofing.

Overall, sheep’s wool insulation offers a triple advantage — exceptional R-value, sound absorption, and it’s an eco-friendly solution. Therefore, it makes sense to use it in applications where insulation and soundproofing are required.

Sheep’s Wool as a Carbon Fiber Precursor

Carbon fibers are used in composite materials and textiles. These fibers are extremely strong, stiff, and light, making them ideal for aerospace, automotive applications, and sporting goods.

In building, carbon fibers are suitable for windows, exterior trim, door systems, columns, pergolas, and fences.

Polyacrylonitrile, a propylene product, has long been the primary carbon fiber precursor.

Unfortunately, polyacrylonitrile production is unsustainable as it consumes more energy while emitting greenhouse gasses into the atmosphere.

Moreover, the fabrication of carbon fibers is a slow and expensive process.

To reduce cost and improve the efficiency of carbon fiber production, some manufacturers have started using sheep’s wool as a precursor for making the fibers.

Using sheep’s wool as the raw material reduces production costs significantly, conserves energy, and helps reduce carbon emissions.

How Do You Turn Sheep’s Wool Into Insulation?

Turning sheep’s wool into insulation is a stepwise process that must be done in a specific order to achieve a quality insulating material with high R-values.

The following is the process of turning sheep’s wool into insulation:

Step 1: Sourcing the Raw Material

A farmer shearing a sheep with an electric clipper.
Sheep must be sheared every spring, which provides the raw material for the sheep’s wool insulation.

Sheep’s wool, the main raw material, is sourced sustainably from farmers who rear sheep for wool production.

The sourcing process involves shearing sheep to remove their woolen fleece.

Step 2: Sorting and Packing the Wool

Once the sheep’s wool is ready, it’s sorted according to color.

Wool can be white, gray, or black.

White wool is highly preferred due to its adaptability to dying.

The wool is then packed in pressed bales and marked to describe the content. Some of the marking details include color, fiber thickness, and length.

The bales are then transported to the scouring plant for further processing.

Step 3: Blending and Cleaning

Once at the scouring plant, the bales are opened to blend the woolen fibers into the required specifications.

The blend is then cleaned to remove impurities like vegetable matter, lanolin, grease, and dirt. The cleaning process involves washing, scouring, and rinsing in warm water to ensure the wool is clean and free from contaminants.

Step 4: Protecting and Fire Retarding

A closeup of a sheep's fleece with a symbol showing a flame on a yellow background with a red circle and diagonal red line across it.
Sheep’s wool is moderately resistant to fire already, but further treatments can make it even more fire-resistant.

After cleaning and drying the wool, it’s time to treat the fibers to make them more fire retardant and resistant to insects and rodents.

This is done by adding boron, ammonium sulfate, or aluminum hydroxide solution.

Ionic liquids can also be used as fire-retardants.

Step 5: Carding

Carding involves combining the dried wool to ensure all the fibers are aligned to create a uniform web of wool. This is essential to ensure that the insulation is consistent in thickness and density.

The resulting product is layered several times to attain the desired thickness.

Step 6: Felting

The carded wool is felted to create a cohesive mat of wool fibers. The process involves matting the wool fibers using heat, moisture, and pressure.

The resulting product is a dense, malleable material that can be easily cut and shaped to fit any space.

Step 7: Drying

A closeup of a sheep's fleece with blue droplet icons and arrows overlain to indicate drying.
The fleece is dried, making it more fluffy and preparing it for the next stage of the process.

The wool is dried to remove any excess moisture.

The drying process involves exposing the wool to heat and air to evaporate moisture. The process also makes the wool fluffy and resilient.

Step 8: Spinning

The wool is spun into yarns of different weights and thicknesses. These yarns are woven into fabrics and then cut to the desired specifications by an automated machine.

The fabric is then quilted with a fire-resistant backing material to create insulation with outstanding thermal properties.

The finished product is then packaged and ready for use in interior walls, the automotive industry, and other applications where insulation is required.

How Long Does Sheep’s Wool Insulation Last?

Sheep’s wool insulation lasts approximately 60 years. Being a natural material, the fibers of sheep’s wool hold together well and don’t degrade due to ultraviolet (UV) light, temperature changes, or humidity like other synthetic insulation materials do.

This makes sheep’s wool insulation a reliable choice for insulating your home or business.

Moreover, the natural fibers help reduce sound transmission, which adds another layer of comfort throughout its 60-year life.

Is Wool Insulation Expensive?

A sheep's fleece with a dollar icon with upwards-pointing arrow overlain.
Sheep’s wool insulation is a little more expensive than certain other types of insulation. However, the cost might be worth it for the sustainability and excellent R-values.

Wool insulation is more expensive than other insulation materials on the market. The cost of wool insulation per square foot ranges from $1.10 to $3.10. On the other hand, mineral wool costs between $1.40 and $2.10 per square foot.

Spray foam and fiberglass insulations cost between $1.25 to $1.50 and $0.88 to $1.64per square foot, respectively.

Cellulose insulation is the cheapest of all, with its prices ranging from $0.60 to $2.30 per square foot.

Although wool insulation is more expensive than the rest, its long-term energy savings are worth the investment. The higher R-value of wool insulation means you’ll save more on energy bills than someone who uses an equivalent thickness of fiberglass or spray foam insulation.

What’s more, wool fibers have excellent thermal performance that will help maintain stable temperatures in your home or business throughout the year.

Benefits of Sheep’s Wool Insulation

The following are the main benefits of using sheep’s wool insulation:

Excellent Thermal Resistivity

A the time of writing, energy costs are at an all-time high. For instance, the average electricity cost in the U.S. is 10.42 cents per kilowatt-hour. As a result, we are all looking for ways to reduce our household’s energy consumption.

One way to lower your energy consumption is by investing in insulation with high thermal resistance.

Sheep’s wool insulation has excellent thermal resistance due to its low thermal conductivity. Therefore, regardless of the season, it helps keep the indoor temperature constant, reducing the demand for heating and cooling.

It Contributes to Sustainability

Wool is a sustainable material that doesn’t deplete natural resources.

Besides consuming less energy, wool insulation manufacturing generates fewer greenhouse gas emissions to pollute the environment.

Moreover, wool is a natural material that degrades easily at the end of its life. This makes sheep’s wool insulation an excellent choice for anyone looking to incorporate sustainable living into their lives.

It is Fire Resistant

Contrary to popular belief, sheep’s wool is fire-resistant.

Sheep wool fibers have high moisture, which makes them naturally fire-resistant.

Furthermore, sheep’s wool has a high nitrogen content of about 16 percent, making it a self-extinguishing material.

With a self-ignition temperature of 560 to 600℃ (1,040 to 1,112℉), sheep’s wool is more than twice as good as wood in fire resistance.

Excellent Acoustics

A microphone in a professional recording studio over a sheep's fleece background.
As well as being great for thermal insulation, sheep’s wool gives an impressive acoustic performance, too.

The sound-absorbing qualities of sheep’s wool insulation make it an ideal choice for acoustic applications.

The natural fibers help reduce reverberation in a room, resulting in better speech intelligibility and fewer echoes from sounds.

This makes sheep’s wool insulation an excellent choice for home theaters and music studios.

Additionally, the material helps reduce background noise from outside sources due to its high noise reduction coefficient.

So, Why Should We Use Sheep’s Wool Insulation?

We should use sheep’s wool insulation because it’s an effective and safe option to reduce energy bills and enhance a room’s acoustic performance.

This insulation provides excellent thermal insulation with fire-resistance and soundproofing qualities.

It’s also a renewable, sustainable building material, so as a result, we can enjoy a comfortable home or workspace while contributing to a more sustainable environment.

Before you leave, check out these companies that make sheep’s wool insulation.

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