Fiberglass vs. Cellulose: Which Works Best as a Blow-In Insulation Material?

Worker insulating the wallAccording to the United States Environmental Protection Agency (US EPA), homeowners can save an average of 11% on total energy costs by air sealing their homes and adding insulation in attics and basements. One way to do this is through blow-in insulation. This is when loose-fill material is blown into your attic through a hose, using a truck-mounted or portable machine. This method of adding insulation is used both for new constructions and existing attics.

There are many kinds of insulation that you can use in your home’s attic, walls, and basements, but the two most common and least expensive are fiberglass and cellulose. Both materials improve your home’s energy efficiency but do so in different ways.

Here are some of the differences between the two insulation materials, so that you can make an informed decision on which one is best for your home.


Though, of course, the prices vary from contractor to contractor, fiberglass, and cellulose are generally inexpensive. They are the cheapest insulation options available in the market today. The difference between their prices is negligible.


R-Value is the measurement of an insulation material’s ability to block thermal transfer or the movement of heat. The higher the R-value, the more insulative the material. Fiberglass and cellulose have similar R-values when installed properly. If so, they perform usually at the 3.5 to 3.7 range. This can still vary based on a lot of other factors, such as wind-washing, settling, or outside temperature, however.

Air Leakage

Both fiberglass and cellulose help retain heat but neither acts as an air barrier. Air can circulate through the insulation. Fiberglass traps air in the pockets of the insulation, while, cellulose can slow air flow, particularly in walls.


Neither insulation material works well when wet or damp. This is because both of them are fibrous, which means they easily trap moisture. However, both can also dry out very quickly because of their high air permeability.


Fiberglass and cellulose have different issues with fire. Since fiberglass is made of spun glass, it won’t burn; when faced with extreme heat, it will simply melt. Blow-in fiberglass is completely non-flammable.

On the other hand, cellulose insulation is made of ground-up paper. Though this paper is treated with flame retardants, there is still a possibility that it would catch fire around recessed lighting and in extreme heat.


Both cellulose and fiberglass are quite durable. While cellulose is treated to help prevent rot, mildew, and decay, fiberglass simply does not rot, nor does it promote mildew or decay. Excessive moisture may cause both to develop these issues, however.

Which Will You Pick?

Choosing the insulation material largely depends on the project at hand. Fiberglass and cellulose have their own pros and cons, and each works differently in distinct applications.

If you opt for blow-in blanket insulation in Kansas City, get in touch with A+ Insulation. We have been insulating homes and businesses in Kansas City since 2004. Our team of experts would love to hear from you and discuss all available options. Contact us today!