The Story of Wool Insulation

by Andrew W. Legge

The use of wool for insulation has an ancient and storied history. The earliest known use of wool in construction likely occurred in regions where sheep were domesticated, thousands of years ago in the bronze age. Wool has always been valued for its natural characteristics: its ability to trap heat, manage moisture, dampen sound, and provide comfort in varying climates.

Trapping Heat

Wool insulation possesses remarkable thermal properties. The natural fibers in wool create tiny air pockets that effectively trap heat, providing excellent thermal performance. This capability helps maintain a stable indoor temperature, reducing the energy needed for heating in winter and cooling in summer.

The R-value, which measures thermal resistance, of wool insulation is competitive with synthetic materials. Wool can achieve R-values ranging from 3.5 to 4.3 per inch, making it an outperformer and suitable for a variety of building applications. Moreover, wool has the unique ability to regulate moisture levels in the air, contributing to a comfortable indoor environment.

Fire Resistance

When it comes to fire safety, wool insulation offers significant advantages. Wool is inherently fire-resistant and has a high ignition point compared to many other materials. This means that in the event of a fire, wool does not ignite easily and can slow the spread of flames, providing vital extra time for evacuation and fire response.

Acoustic Properties

Wool insulation excels not only in thermal performance but also in sound absorption. The dense, fibrous structure of wool helps to dampen sound waves, making it an effective barrier to noise. This benefit is particularly advantageous in modern urban living, multi-family dwellings, or commercial spaces where noise reduction is a priority.

By incorporating wool insulation into walls, roofs, floors and aesthetic sound panels builders can create quieter spaces that enhance comfort and productivity. Moreover, the sound-dampening properties do not diminish over time, ensuring long-term acoustic performance.

Moisture Management

Wool insulation has a unique property known as "breathability." This means that it can effectively manage moisture, allowing water vapor to pass through while preventing substantial moisture accumulation. This characteristic helps mitigate the risk of condensation, mold, and decay that can occur in more moisture-retentive materials.

In fact, wool can absorb significant amounts of moisture—up to 30% of its weight—while still remaining dry to the touch. This remarkable absorption capacity plays a crucial role in temperature regulation. When humidity levels are high, wool insulation traps moisture from the air, mitigating excessive dampness. Conversely, when the air is drier, wool releases the stored moisture back into the environment. This absorption and release cycle helps to stabilize indoor humidity levels, a feature that is beneficial in both modern residential and commercial applications.

Overall, combining traditional practices with modern advancements in sustainable building has made this classic material resurge, although looking at its history, it never should have gone away.

Textiles Rise

With the rise of textile manufacturing in the 18th and 19th centuries, wool became more widely available and affordable. During this period, wool insulation was utilized in various building projects but was not yet standardized. Craftsmen and builders often improvised materials, using waste wool from textiles to create draft-proofing materials for homes and commercial buildings. This period also saw the first small-scale experimentation with wool insulation in the building trade, as artisans understood its potential to improve indoor climates. British Parliament and Edinburgh Castle are both known to be insulated with wool.

The true leap in wool insulation technology occurred in the 20th century. It began with increased awareness of energy efficiency and sustainable building practices leading to a renewed interest in natural materials like wool.

The process continued in the post-World War II era, with a push for better housing quality, which included a focus on insulation. Alternative materials such as fiberglass and foam began to dominate the market, their manufactured convenience often overshadowing traditional insulation materials like wool. However, these synthetic alternatives often present challenges such as health risks, environmental concerns, and inefficiencies in energy use.

As a result, researchers and builders began to rediscover wool's unique insulating properties, particularly with increasing environmental awareness during the 1970s energy crisis. The wool industry responded by promoting wool insulation as a natural, sustainable alternative to synthetic insulation materials. Advances in wool processing technology enabled wool insulation products to be created in batts, rolls, and loose-fill forms, enhancing ease of application.

Sustainability and the 21st Century

As sustainability has gained prominence in the 21st century, wool insulation has experienced a meaningful resurgence. Modern consumers are increasingly seeking eco-friendly building materials, and wool fits these criteria exceptionally well. Moreover, the sustainable farming practices associated with wool production, as well as its biodegradability, make it a desirable choice for eco-conscious builders and homeowners.

It does require cleaning, which goes better in volume. That’s one reason we procure our wool in New Zealand. NZ is responsible for some 11% of the global clip, making the cleaning process more efficient and reliable.

Also naturally occurring is an increased global awareness of climate change and energy conservation has driven interest in wool insulation, prompting ongoing research into its performance and efficiency in contemporary building practices. As a result, wool is very much in the conversation pertaining to sustainable architecture and renewable materials.

What are the modern advantages of wool that will drive the growth in the market? The list is extensive yet the myriad of modernly discovered benefits might be best headlined as follows: environmental impact, health benefits, durability,  and ease of installation.

Environmental Impact

One of the most significant advantages of wool insulation is its sustainability. Wool is a natural product, primarily sourced from sheep, and its production has an exceptionally low carbon footprint compared to synthetic alternatives. The wool industry promotes sustainable farming practices, which ensure that sheep are raised without harmful chemicals or harmful environmental impacts.

Furthermore, wool is biodegradable, meaning that at the end of its life cycle, it can break down naturally without contributing to landfill. In contrast, synthetic insulation materials often take centuries to decompose and can release harmful chemicals into the environment during this process. Also relevant is the ability to use less material and achieve the same or better performance when using wool insulation. For example, wool will exceed the R-value of cellulose in a 2x4 or 2x6 with <1 lb. per cubic feet of material whereas cellulose would require a density of ~3.5lbs per cubic foot. By choosing wool insulation, builders and homeowners support a more sustainable approach to construction and renovations

Health Benefits

Wool insulation also offers significant health and comfort benefits. Conventional insulation materials, particularly those made from fiberglass or synthetic fibers, can release volatile organic compounds (VOCs) and other irritants into the indoor air, negatively impacting air quality. In contrast, wool does not contain harmful synthetic chemicals and has been shown to contribute to improved indoor air quality by bonding with harmful chemicals such as formaldehyde, NOx and SO2.

Additionally, wool is naturally hypoallergenic, making it an excellent choice for individuals with respiratory issues or allergies. It does not promote the growth of mold or mildew, which are often exacerbated by moisture retention in other insulation types. By using wool insulation, homeowners can create a healthier living space for themselves and their families.

Durability and Longevity

Another benefit of wool insulation is its long-lasting nature. Wool fibers are resilient and can withstand wear and tear better than synthetic materials, particularly in the face of moisture. Unlike fiberglass, which can degrade over time, wool maintains its insulating properties and structural integrity.

With proper installation, wool insulation can last for decades, providing ongoing thermal performance and energy savings without the need for replacement. This longevity translates to cost savings over time, as homeowners won't need to invest in regular upgrades or replacements.

Admittedly, wool is pricier than the cheapest insulation materials but it's quite competitive with higher-end materials. In general fiberglass and cellulose are the cheapest while mineral wool, foam, and havelock wool tend to be together at the upper end of the cost spectrum.  Wool tends to be cheaper than mineral wool, but the durability of wool makes it worth a higher initial investment.

Easy Installation

Wool insulation is also easier to handle and install than some synthetic alternatives. It is available in loose-fill or batts that can be cut to size, making it suitable for various applications, including walls, ceilings, and floors. The flexibility of wool allows it to easily fit into odd spaces or around plumbing and electrical fixtures, minimizing the need for additional materials or labor.

Wool for the Win

In sum, wool insulation has a rich and varied history that spans across cultures and centuries. It is arguably the most dynamic fiber on the planet. From its early use in ancient dwellings to its modern resurgence as a sustainable building material, wool insulation is valued for its exceptional thermal and acoustic properties, health benefits, and eco-friendliness. As the construction and insulation industries continue to evolve, wool remains a vital choice for those committed to sustainability, comfort, and indoor air quality in both residential and commercial applications.

About the author

Andrew is founder and managing partner of Havelock Wool. He has a passion for all things New Zealand, where the company procures its wool, mirrored by a desire to affect positive change in the built environment. He has lived and traveled around the world and seeks to leverage those experiences in bringing a biophilic, best practice to an industry known to contribute excessive waste to our world.