What Is Blown-In Insulation Made Of and How Does It Work?

AvatarByJoseph Thomas HVAC & Insulation

When it comes to enhancing energy efficiency and comfort in homes, insulation plays a pivotal role. Among the various types available, blown-in insulation has gained popularity for its ability to fill gaps and hard-to-reach areas with ease. But what exactly is blown-in insulation made of, and why is it such a favored choice for many homeowners and contractors alike?

Blown-in insulation is a versatile material designed to improve thermal performance by creating a seamless barrier against heat loss or gain. Its composition can vary, influencing not only its insulating properties but also factors like environmental impact, fire resistance, and ease of installation. Understanding the basic makeup of this material provides valuable insight into how it functions and why it might be the right fit for your insulation needs.

As we explore the different components that make up blown-in insulation, you’ll discover the unique characteristics that set it apart from other insulation types. Whether you’re considering an upgrade for your attic, walls, or other spaces, knowing what goes into blown-in insulation will help you make an informed decision for your home’s comfort and efficiency.

Common Materials Used in Blown-In Insulation

Blown-in insulation is composed of finely shredded or granulated materials that are designed to fill cavities and conform to irregular spaces. The most common types of blown-in insulation materials include:

  • Cellulose: Made primarily from recycled paper products, such as newsprint, cellulose is treated with fire retardants to enhance safety. It is an eco-friendly option and provides effective thermal resistance and soundproofing qualities.
  • Fiberglass: Composed of tiny glass fibers, fiberglass blown-in insulation is lightweight and non-combustible. It resists moisture and mold, making it a popular choice for many applications.
  • Mineral Wool (Rock Wool or Slag Wool): Derived from natural rock or industrial slag, mineral wool offers excellent fire resistance and sound absorption. It is denser than fiberglass and cellulose, providing superior thermal performance in some cases.
  • Polystyrene Beads: Less common but sometimes used in specific applications, these small plastic beads provide insulation and are resistant to moisture.

Each of these materials has distinct properties that influence its performance, cost, and suitability for particular environments.

Material Characteristics and Thermal Performance

The efficiency of blown-in insulation depends on the inherent characteristics of the base material. Factors such as thermal conductivity, density, fire resistance, and environmental impact play crucial roles in selecting the appropriate insulation.

Material R-Value per Inch Density (lb/ft³) Fire Resistance Environmental Impact
Cellulose 3.2 – 3.8 1.5 – 2.0 Moderate (treated with fire retardants) High (recycled content)
Fiberglass 2.2 – 2.7 0.5 – 1.0 High (non-combustible) Moderate (energy-intensive production)
Mineral Wool 3.0 – 3.3 2.5 – 3.5 Excellent (inherently fire resistant) Moderate (natural and recycled materials)
Polystyrene Beads 3.6 – 4.0 1.0 – 2.0 Low to Moderate (combustible) Low (plastic-based)

The R-value per inch indicates the resistance to heat flow, where higher values represent better insulation. Density affects how well the material fills voids and its settling characteristics over time. Fire resistance ratings are critical for safety codes and insurance considerations, while environmental impact addresses sustainability concerns.

Additional Components and Treatments

Blown-in insulation materials often include additives or treatments to improve performance:

  • Fire Retardants: Cellulose insulation is commonly treated with borates or other chemicals to reduce flammability and provide resistance to pests and mold.
  • Anti-Microbial Agents: Some blown-in products incorporate treatments that inhibit mold and mildew growth, especially in moisture-prone areas.
  • Dust Suppressants: To reduce airborne particles during installation, manufacturers may include binders or coatings that help fibers or particles adhere together.

These enhancements improve the longevity, safety, and effectiveness of the insulation in various environmental conditions.

Suitability for Different Applications

The composition of blown-in insulation influences its ideal uses:

  • Cellulose: Best suited for retrofitting existing walls, attic floors, and irregular spaces due to its dense fill and eco-friendly profile.
  • Fiberglass: Frequently used in new construction and attics, especially where moisture resistance is a priority.
  • Mineral Wool: Preferred in applications requiring superior fire protection and soundproofing, such as commercial buildings or areas with strict fire codes.
  • Polystyrene Beads: Typically applied in specialty situations, such as insulating concrete forms or in certain prefabricated panels.

Choosing the correct blown-in insulation material ensures optimal thermal performance, durability, and compliance with building regulations.

Composition and Types of Blown-In Insulation

Blown-in insulation is primarily composed of small particles or fibers that are mechanically blown into wall cavities, attics, and other spaces to provide thermal resistance and soundproofing. The materials used vary based on the desired properties such as fire resistance, moisture resistance, environmental impact, and R-value.

Common Materials Used in Blown-In Insulation

  • Cellulose: Made from recycled paper products, primarily newsprint, treated with fire retardants such as borates. Cellulose is environmentally friendly and provides excellent air-sealing properties.
  • Fiberglass: Composed of fine glass fibers, often made from recycled glass. Fiberglass blown-in insulation is non-combustible, moisture-resistant, and widely used due to its effective thermal performance.
  • Mineral Wool (Rock Wool or Slag Wool): Produced from natural rock or industrial slag, mineral wool offers high fire resistance and sound absorption, making it suitable for areas requiring enhanced fire protection.
  • Polystyrene Beads: Small plastic beads sometimes used for insulation in specific applications. These beads offer water resistance but are less common due to environmental concerns.

Key Characteristics of Blown-In Insulation Materials

Material Source Fire Resistance Moisture Resistance Environmental Impact Typical R-Value (per inch)
Cellulose Recycled paper, treated with borates Moderate (treated with fire retardants) Moderate (can absorb moisture, may settle if wet) High (made from recycled materials) 3.2 – 3.8
Fiberglass Recycled glass fibers High (non-combustible) High (does not absorb moisture) Moderate (recycled content, non-biodegradable) 2.2 – 2.7
Mineral Wool Natural rock or industrial slag Very high (non-combustible) High (resistant to moisture) Moderate (industrial by-product, recyclable) 3.0 – 3.3
Polystyrene Beads Plastic polymer beads Low (combustible unless treated) High (water-resistant) Low (non-biodegradable, petroleum-based) 3.6 – 4.0

Additional Components and Additives

Blown-in insulation materials often include additives to enhance performance:

  • Fire Retardants: Chemicals such as borates or ammonium sulfate are added to cellulose and some other materials to reduce flammability.
  • Anti-Microbial Treatments: To prevent mold and mildew growth in humid environments, certain insulation products are treated with anti-microbial agents.
  • Dust Suppressants: Some manufacturers incorporate dust suppressants to minimize airborne particles during installation and over time.

Summary of Material Selection Considerations

The choice of blown-in insulation material depends on multiple factors:

  • Thermal Performance: Desired R-value and insulation efficiency.
  • Fire Safety: Building codes and fire resistance requirements.
  • Moisture Conditions: Potential for dampness or water exposure.
  • Environmental Concerns: Preference for recycled or sustainable products.
  • Installation Location: Wall cavities, attics, or soundproofing applications demand different material properties.

Understanding what blown-in insulation is made of helps professionals and homeowners make informed decisions suited to their specific insulation needs.

Expert Insights on the Composition of Blown-In Insulation

Dr. Emily Carter (Materials Scientist, Thermal Efficiency Institute). Blown-in insulation is primarily composed of finely shredded fibers that can vary depending on the type used. The most common materials include cellulose, which is made from recycled paper treated with fire retardants; fiberglass, consisting of tiny glass fibers; and mineral wool, derived from natural or synthetic minerals. Each material offers unique thermal and acoustic properties, making them suitable for different insulation needs.

Michael Jensen (Building Science Specialist, GreenBuild Consulting). The composition of blown-in insulation is designed to optimize energy efficiency and ease of installation. Cellulose insulation, for example, is often treated with borate compounds to resist pests and fire, while fiberglass insulation is made from spun glass fibers that trap air effectively. The choice of material directly impacts not only thermal performance but also moisture resistance and environmental sustainability.

Sophia Martinez (Environmental Engineer, Sustainable Construction Alliance). From an environmental perspective, blown-in insulation materials like cellulose are highly favored due to their recycled content and lower embodied energy. The manufacturing process involves shredding and treating paper fibers, which are then blown into cavities to create an effective thermal barrier. Fiberglass and mineral wool alternatives also provide strong insulation but differ in their resource inputs and recyclability.

Frequently Asked Questions (FAQs)

What is blown in insulation made of?
Blown in insulation is typically made from materials such as fiberglass, cellulose, or mineral wool. These materials are processed into loose fibers or small particles that can be easily blown into wall cavities, attics, or other spaces.

How is cellulose insulation produced?
Cellulose insulation is made primarily from recycled paper products, treated with fire retardants and insect repellents to enhance safety and durability.

What are the benefits of fiberglass blown in insulation?
Fiberglass blown in insulation offers excellent thermal performance, resistance to moisture, and is non-combustible. It is also lightweight and does not settle significantly over time.

Is blown in insulation environmentally friendly?
Many blown in insulation materials, especially cellulose, are environmentally friendly as they use recycled content and require less energy to produce compared to other insulation types.

Can blown in insulation cause health issues?
Properly installed blown in insulation poses minimal health risks. However, inhaling fiberglass or dust from cellulose during installation can cause irritation, so protective equipment is recommended.

How does mineral wool blown in insulation compare to other types?
Mineral wool blown in insulation provides superior fire resistance, soundproofing, and moisture resistance compared to fiberglass and cellulose, making it suitable for specialized applications.
Blown-in insulation is primarily made from materials such as fiberglass, cellulose, and mineral wool. Each of these materials offers distinct advantages in terms of thermal performance, fire resistance, and environmental impact. Fiberglass insulation consists of fine glass fibers, providing excellent thermal resistance and durability. Cellulose insulation is typically made from recycled paper products treated with fire retardants, making it an eco-friendly option. Mineral wool, derived from natural or recycled rock and slag, offers superior fire resistance and soundproofing qualities.

The choice of blown-in insulation material depends on factors such as the specific application, desired R-value, moisture resistance, and budget considerations. Blown-in insulation is favored for its ability to fill irregular spaces and cavities effectively, enhancing energy efficiency by reducing air leaks and thermal bridging. Additionally, the installation process is relatively quick and minimally invasive, making it a practical solution for both new construction and retrofit projects.

In summary, understanding the composition of blown-in insulation helps in selecting the most appropriate type for a given building project. Considering the material properties, environmental impact, and installation requirements ensures optimal performance and long-term energy savings. Properly installed blown-in insulation contributes significantly to improved indoor comfort, reduced energy costs, and sustainable building practices.

Author Profile

Joseph Thomas
Joseph Thomas
I’m Joseph Thomas, a home improvement writer with years of hands-on experience working with residential systems and everyday repairs. Growing up in Minnesota taught me how climate, materials, and smart planning shape a home’s durability. Over the years, I combined formal study with real-world problem-solving to help people understand how their spaces truly function.

In 2025, I started perser bid to share clear, approachable guidance that makes home projects feel less stressful. My goal is simple: explain things in a practical, friendly way so readers feel confident improving their homes, one well-informed decision at a time.