If you are researching insulation and keep seeing cellulose pop up, you may wonder if this old-school insulation still holds up.
Cellulose insulation has been around for decades and is still used in homes across the country. It is affordable, made from recycled materials, and widely available. But like any insulation product, it comes with strengths and tradeoffs.
If you are comparing options, here is what you need to know about cellulose insulation, how blown-in cellulose insulation works, and whether it makes sense for your home.
• Cellulose insulation is a fiber-based material made mostly from recycled paper or denim.
• Blown-in cellulose insulation is commonly installed in attics and wall cavities.
• The R-Value of cellulose falls between R-3.1 and R-3.8 per inch.
• It slows heat transfer but does not stop air movement.
• It can settle up to 20 percent over time.
• It can absorb significant moisture if exposed to water.
• Chemical treatments improve resistance to fire, pests, and mold.
• Installation quality plays a major role in performance.
So what is cellulose insulation exactly?
Cellulose insulation is a fiber-based insulation material that is typically installed with a blowing machine. It is most often used in:
When homeowners refer to cellulose blown-in insulation, they’re talking about this installation method where loose fibers are blown into a cavity to fill it completely.
Cellulose became especially popular in the 1950s when manufacturers began adding fire-retardant treatments. That added a level of safety and comfort that other insulation options at the time did not offer.
One of the most common questions homeowners ask is, what is cellulose insulation made of?
Cellulose insulation is typically composed of about 75 to 85 percent recycled newspaper or denim. The remaining portion consists of chemical treatments.
If you’re wondering what is in cellulose insulation, those additives are included to improve:
In some new construction applications, moisture is added during installation to help the material adhere to the inside of open wall cavities before drywall is installed.
Another common question is simple: Is cellulose insulation safe?
Generally speaking, yes – when it is properly installed and kept dry.
The fire-retardant treatments are specifically designed to improve safety. However, performance can change under certain conditions.
If cellulose becomes saturated with water, it can:
Dust during installation can also create a mess if containment is not handled properly. As with any insulation material, safety and performance depend heavily on correct installation and proper moisture management.
There are three primary ways in which blown-in cellulose insulation is installed.
Loose-fill cellulose is blown across the attic floor and then raked to ensure full, even coverage.
This is one of the most common applications.
Dense-pack cellulose is blown into enclosed wall cavities or floor systems under pressure.
Dense packing improves performance compared to loose fill, but it still allows some air movement.
In new construction, cellulose can be dampened and sprayed into open wall cavities before drywall is installed.
The added moisture helps it stick in place during installation.
Cellulose provides thermal insulation and can offer some sound-dampening benefits.
But there are some limitations.
The R-Value of cellulose insulation typically falls between R-3.1 and R-3.8 per inch.
That number only measures resistance to heat flow. It does not measure resistance to air movement, and that matters.
Air leakage can account for up to 40 percent of a home’s energy loss. If insulation slows heat but still allows air to move through it, comfort and efficiency suffer.
Choosing insulation based solely on R-Value can be misleading.
Cellulose insulation offers several advantages.
There are also important drawbacks of cellulose insulation to consider.
If you are considering cellulose blown-in insulation, here’s what installation typically involves.
Heating and cooling account for roughly 50 to 70 percent of household energy use.
Cellulose helps reduce heat transfer, but it struggles with airflow control. If air continues to move through the insulation, your HVAC system may have to work harder to maintain comfort.
Over time, settling and moisture exposure can further reduce effectiveness.
Understanding how heat, air, and moisture move through your home is the key to making a smart insulation decision.
Cellulose insulation is affordable, widely used, and made from recycled materials.
It can improve thermal performance and provide sound dampening.
However, it settles, absorbs moisture, and does not stop air movement.
The best insulation decision is not just about R-Value – it is about understanding how heat, air, and moisture interact inside your home. When you look at the full building science picture, you can choose a solution that supports long-term comfort and efficiency.
If you want to learn more about insulation and building science, explore the additional resources in our Learning Center.
What are the Best Exterior Wall Insulation Options?
Cellulose insulation is a fiber-based insulation made primarily from recycled paper products and treated for fire, pest, and mold resistance.
It is commonly installed as blown-in insulation.
It is typically made of 75 to 85 percent recycled newspaper or denim and about 15 percent chemical treatments.
Yes, when properly installed and kept dry.
Moisture exposure can reduce its effectiveness and fire resistance.
Cellulose insulation has an R-Value between R-3.1 and R-3.8 per inch.
No.
It slows heat transfer but does not fully prevent air movement.
Yes.
It can settle up to 20 percent, which may reduce performance.