Cellulose Insulation: Separating Fact From Fiction

FACT: Properly installed cellulose is designed to account for settling.

Loose-fill cellulose is installed to a specified depth and density, with the installation accounting for expected settling. Dense-packed cellulose is installed under pressure to achieve the required density within the cavity.

Proper installation is critical to achieving the intended coverage and performance.

The takeaway: Cellulose does not have an automatic "settling problem." Installation density, coverage, and proper application are what matter.

FACT: Properly manufactured and installed cellulose is designed to provide insulating performance for the life of the home.

There is no 20-year expiration date on the insulating value of cellulose.

Properly manufactured and installed cellulose is not designed to gradually "wear out" as an insulator simply because it gets older. Under normal conditions, its insulating performance is intended to continue for the life of the structure.

The takeaway: The claim that cellulose "only lasts 20 years" is misleading. Properly installed cellulose is designed to provide insulation performance for the life of the home.

FACT: The mineral treatment is an integral part of properly manufactured cellulose insulation.

Cellulose is treated with mineral-based fire retardants and pest-resistant additives during manufacturing. These treatments are incorporated DIRECTLY into the insulation rather than being a temporary surface coating.

The treatment does not simply "degrade" because the insulation gets older.

As with any building material, prolonged exposure to unusual conditions such as significant water infiltration can affect the material and should be addressed.

The takeaway: Properly manufactured cellulose is designed to retain its treated properties throughout its service life when kept in appropriate building conditions.

FACT: Cellulose itself does not automatically cause mold growth.

Mold requires the right combination of moisture, temperature, and an available food source.

Modern cellulose insulation is treated with mineral additives designed to inhibit fungal growth. More importantly, a properly designed wall or attic assembly should control bulk water and condensation regardless of the insulation material being used.

If a building assembly remains chronically wet, the solution is to identify and correct the moisture problem—not simply blame the insulation.

The takeaway: Cellulose does not create a moisture problem. Proper moisture control and building-envelope design are essential to preventing mold.

FACT: Properly manufactured cellulose is treated with mineral additives that make it a poor environment for many insects and pests.

The paper fibers used to make cellulose insulation may sound like something pests would want to nest in, but finished cellulose insulation is very different from untreated paper.

Cellulose is treated with mineral-based additives that make the insulation a less favorable environment for insects and other pests. Borate compounds are well established for their ability to discourage a range of insects and rodents. 

Cellulose also has a physical advantage in attic applications: its dense, interlocking fiber structure doesn't provide the same loose, fluffy nesting environment (including some other insulation types), that many rodents can take advantage of.

The takeaway: Cellulose isn't simply "recycled paper sitting in your attic." Properly manufactured cellulose is mineral-treated and densely installed, creating an environment that is generally less attractive to pests and insects.

FACT: Cellulose is manufactured with fire-retardant mineral treatments.

Although cellulose is made primarily from recycled paper fibers, the finished insulation is treated with mineral fire retardants.

When exposed to fire, cellulose does not behave like untreated loose paper. The treated fibers char and form a protective layer that help slow heat transfer and flame propagation.

Fire performance ultimately depends on the entire building assembly, including drywall, framing, air barriers, insulation, and other components.

The takeaway: Being made from paper does not mean cellulose behaves like ordinary paper when used as properly manufactured insulation. Its mineral fire-retardant treatment and dense fiber structure give it significant fire-performance advantages. Real-world comparative demonstrations, such as The Big Burn, have shown cellulose-insulated assemblies providing substantially greater fire resistance than comparable fiberglass-insulated assemblies. 

FACT: R-value is only one part of insulation performance.

Cellulose provides competitive thermal resistance at R 3.7/in. Higher total R-values can be achieved by increasing the installed thickness. Its real-world performance is influenced by more than just the laboratory R-value printed on the package.

Density, installation quality, air movement, thermal mass, coverage, and the performance of the entire building assembly all matter.

This is particularly important in attics, where continuous coverage can also help reduce the effect of thermal bridging through framing.

The takeaway: Don't judge an insulation system by R-value alone. Look at how the material performs as part of the complete building envelope.  The R-value tells you how strongly the material resists conductive heat flow, but it doesn't tell the whole story about how an insulation system performs in a real home. For more information visit our Making The Right Choice page.

FACT: Modern cellulose insulation is an engineered building product.

Cellulose is manufactured primarily from recycled paper fibers, but it is not simply loose newspaper blown into a wall or attic.

The material is processed, fiberized, and treated with mineral additives to provide the properties required for use as building insulation.

Its density and installation method are also carefully controlled depending on the application.

The takeaway: Recycled paper is the raw material—not the finished product.

FACT: Attic structures are designed and evaluated for their intended loads.

Cellulose is denser than many loose-fill fiberglass products, which means it adds slightly more weight per square foot.

That does not automatically make it unsuitable for an attic.

Proper installation means considering the existing structure, insulation depth, access, and other relevant building conditions.

The takeaway: The question isn't simply whether cellulose is heavier. The question is whether the existing structure and application are appropriate for the intended insulation load.

FACT: Cellulose can perform extremely well in cold climates.

Cold-weather performance isn't determined by R-value alone.

Dense, interlocking cellulose fibers provide significant resistance to internal air movement and wind-washing. Its density can also provide advantages in controlling convective air movement within the insulation layer.

The takeaway: Cellulose is well suited to cold climates when the insulation and air barrier are properly installed.

FACT: Cellulose's ability to buffer moisture can be an advantage when the assembly is properly designed.

Cellulose is hygroscopic, meaning its fibers can temporarily absorb and redistribute small amounts of water vapor.

This is different from allowing bulk liquid water to remain trapped inside a wall.

A properly designed wall assembly still needs effective control of bulk water, air leakage, and vapor movement. No insulation should be expected to compensate for a leaking roof, plumbing failure, or major water intrusion.

The takeaway: Moisture buffering is not the same thing as causing rot. Proper building-envelope design and moisture management remain essential. Regardless of the insulation type, if bulk water infiltration occurs, rot, mold, and fungal growth are a possibility.

FACT: Installation requires appropriate equipment and practices, but the finished product is designed for use inside buildings.

Like many blown insulation products, cellulose creates airborne dust during installation.

Professional installers use appropriate equipment and installation practices to manage that dust and curb infiltration during installation.

Once installed and contained within the building assembly, the insulation is no longer being mechanically blown around the home.

The takeaway: Installation conditions are different from the finished product. Proper equipment, containment, and installation practices matter.

FACT: Cellulose has a long history—and modern cellulose is an engineered insulation product.

Cellulose has been used as insulation for many years, but the product and installation methods have evolved.

Today's cellulose products are manufactured with controlled fiber characteristics and mineral treatments and are installed using equipment designed for specific applications.

Its recycled content, density, thermal characteristics, acoustic performance, and moisture-buffering properties continue to make cellulose a highly relevant and sought-after option for modern building assemblies.

The takeaway: A long history doesn't make a building product outdated. What matters is how the modern product is manufactured, specified, and installed.