Cellulose vs Fiberglass

Insulation Materials


Long ago there were several insulation materials available: Rockwool, Vermiculite, Fiberglass, Cellulose, Mineral-Wool, all sorts of stuff. Over the years we’ve seen many come and go; they were found to be dangerous, ineffective or impractical. Today there are basically two choices: Fiberglass and Cellulose. The confusing thing is that Fiberglass is available in two forms: rolled batting or blown, and Cellulose is only available as a blown material. It’s not that difficult to figure out which one is best.
Blowing - attic insulation


Materials Comparison Cellulose vs. Fiberglass


Blowing Insulation


  • Lifetime guarantee
  • Non-toxic, safe
  • No itching
  • Rodent resistant
  • Insect resistant
  • Mold/mildew resistant
  • 8.1″ to attain an R30
  • Soundproofing
  • Soft material
  • Non-flammable
  • Bland grey color



  • No Guarantee
  • Hazard-warning label
  • Very itchy & irritating
  • Rodents nest in it
  • No resistance to insects
  • No resistance to mold/mildew
  • Requires almost 12″ for R30
  • Minimal soundproofing
  • Rigid glass fibers
  • Merely melts in a fire
  • Vibrant pink yellow or white color
Rolled fiberglass






Cellulose is only available as a loose-fill (blown) material. We consider it the most effective, efficient, longest-lasting and safest material you can use. Cellulose has many advantages over fiberglass; it has a lifetime warranty, is permanently non-flammable and resistant to rodents, insects and mold. It also has soundproofing qualities and does not itch. Best of all, cellulose is non-toxic, safe and environmentally friendly.

Cellulose has many advantages over fiberglass. Cellulose attains an R-30 rating with 8.1-inches of thickness, whereas fiberglass needs be about 12-inches thick to achieve the same performance, this makes cellulose far more effective per inch. Unlike fiberglass, cellulose has no hazard/warning labels. The product is rigorously tested and approved by the Consumer Products Safety Commission, OSHA and the Underwriters Laboratories, UL label.

Cellulose is made from reconstituted wood fiber product, which includes newspaper, cardboard and other wood related products. While some would imagine this to be flammable, the cellulose is treated with borate to be permanently non-flammable. Cellulose carries an ASTM Class 1 rating and meets specifications set by federal, state and local building authorities for being non-flammable. You can actually hold a match or torch to the product and it will not burn!


An additional benefit of the cellulose being treated with borate is that it is resistant to insects, rodents, molds, mildew and fungus. Cellulose is also very earth-friendly in that it is made from almost entirely recycled products. Cellulose also has excellent sound-reducing qualities too, homeowners frequently report a quieter home after it’s insulated.

For more information on cellulose, check out these websites:

www.greenfiber.com , www.cellulose.orgwww.ornl.gov – Department of Energy

Handful of Cellulose


Fiberglass is available in two forms: as batting (rolled) or as a loose-fill (blown) material. Many homeowners typically feel they want rolled insulation, but once they do the research they find otherwise. Fiberglass insulation, whether rolled or blown, has several negative characteristics of significant concern. Please do your research before using fiberglass!

Fiberglass is glass fibers; the fibers are very small, rigid and sharp. On account of this, all fiberglass products have a hazard/warning label on them clearly relating to the danger of cancer, upper respiratory irritation and other related illness. Anyone who has ever worked with fiberglass can attest to the terrible “itch”. Contractors or workman are often hesitant or charge more to work in an attic that has fiberglass.


Homeowners often feel that the attic area is separate from their homes living quarters, but the increased use of recessed lighting, HVAC units and other devices located in the attic has lead to a surprising amount of air interaction between attic area and living quarters below. When a home develops health issues for the occupants, environmental companies are quick to remove fiberglass insulation from the attic or at least blow Cellulose insulation over the Fiberglass to seal and encapsulate it.
Fiberglass Attic

Fiberglass does not carry a lifetime warranty. Blown fiberglass is known for settling and packing after it’s installed. Much like the cotton-candy that it resembles, the very nature of blowing Fiberglass tends to fluff the material up, the product then settles over time. The rolled fiberglass minimizes the fluffing-effect, but the rolled-in application by its nature is several strips that run between the ceiling joist. It doesn’t seal over the top of the framing and has a compromised fit around the plumbing, piping and conduit that runs throughout the attic, so while the rolled Fiberglass won’t settle and pack as much, it’s a compromised fit to begin with.

Also, Fiberglass is less efficient as compared to cellulose; fiberglass must be over 12″ thick to produce an R-30 rating, while cellulose only needs to be 8.1″ in order to attain the same R-30 performance. Anyone who has been in an attic can tell you it’s more difficult to work in a foot-thick of itchy Fiberglass then 8″ of soft Cellulose!

Fiberglass does not have any insect or termite resistant qualities, in fact, fiberglass makes a splendid home for rodents and vermin. Quite often we find evidence of rats and mice living in the fiberglass. Given some moisture, fiberglass also provides an excellent media for mold & mildew to grow and foster. By comparison, Cellulose is mold, mildew and fungal resistant, as well as rodent and insect resistant.

Blown vs. Rolls (Batting)

Fiberglass rolls (or batts) are useful in that they can be hung under floors or used in open-framing and in new construction situations. But once a home is built it can either be rolled with batting OR blown with a loose-fill (fiberglass or cellulose) material. A blown application offers several advantages over batting.

Many homeowners assume batting is better, or they’re drawn to what appears to be a cleaner job. Some homeowners are directed by their trusty contractor while others just feel a sense a familiarity towards the rolls. The truth of the matter is that rolled fiberglass is often installed during construction merely because it’s convenient. When homeowners, contractors or architects do some research, cellulose blown insulation easily emerges as the best choice.

The downfall of rolled material is that it must be placed between each ceiling joist, sometimes fitting tightly, sometimes loosely. Rolled material must go over, under and around the many obstacles in the attic such as plumbing, piping and electrical conduit; this application compromises the performance of the insulation by creating gaps, voids and other “leaks”. The blown application seals and provides a much “tighter” blanket of insulation throughout the attic, this is referred to as a “monolithic fill”, which is a fancy way of saying that the blown material and application offers a continuous blanket of insulation that covers and seals over everything as a solid blanket.

Studies at the University of Colorado have established that a blown-in insulation rated at R-19 provides equal performance to the same job done with R-30 batting. The flip side of this equation is that R-30 batting only renders an R19 in practical effectiveness. So while the rolled material is rated and stamped as R-30, it’s only offering a real performance of R-19.

Another problem arises when an attic already has an old or existing insulation. Most homes at one point or another were insulated with old insulation; rolled material does not lay well over existing insulation, the result is a lot of voids, gaps and a compromised fit. Because of this, only homes that have no existing insulation are candidates to be rolled with fiberglass. Some people figure they can vacuum-out or remove the old insulation, but this is extremely time-consuming, expensive and impractical, the best thing to do is simply add more material on top of the existing insulation to bring the entire attic up to R-30 or R-38.

Another advantage of blowing insulation is that we “shoot” the material up to 20-feet in distance, this allows us to reach all the tight areas that would otherwise not be accessible with batting. We also don’t have to work over every square foot of the attic, thusly reducing the potential for disturbing wiring or placing weight over long stretches of ceiling framing that may cause the ceiling to deflect of crack under the weight of the installers. The blown material reaches the deep corners and covers the entire attic floor.

The most important benefit of blowing insulation is that it allows us to use cellulose insulation instead of a fiberglass product. Cellulose is by far a more effective, efficient, longer lasting and safer material as compared to fiberglass. Please see our materials comparison section for more details.

Cellulose vs. Fiberglass Studies by the University of Colorado

In a two-month study at the University of Colorado School of Architecture and Planning, researchers compared the energy conservation efficiency of two test buildings.

In one building cellulose insulation was installed in the attic and walls. In the second building fiberglass was also installed in the attic and walls. Here are the results:

  • Cellulose achieved a tighter building cavity and cut air infiltration by at least 30% more than fiberglass.
  • When the heat was turned off at night, over a 9 hour period, the cellulose insulated building retained 7 degrees more heat than the fiberglass insulated building.
  • It was estimated that in the temperate climates a cellulose insulated building would require about 26% less energy to heat than a fiberglass insulated building. It was further concluded that the energy benefit would become even more significant in severe climates
  • Cellulose blown-in insulation reduces air leakage more effectively than fiberglass batting or fiberglass blown-in insulation.

Conclusion: Homes insulated with cellulose insulation require considerably less energy to heat and cool then homes insulated with fiberglass. Cellulose is the better insulation.

The Wrong Advice!

Over the years I’ve had a lot of homeowners tell me “I don’t want that blown stuff”. When I ask why they feel that way, it’s one of either two reasons, but the thing you have to remember is that not all blown insulation is the same!

“My contractor told me to stay away from blown insulation”

For many years blown fiberglass was popularly installed in attics, this material actually clings to your clothing and makes your skin itch for days! Just about any electrician, plumber or contractor who has worked in an attic full of blown fiberglass will preach his words of hate and despise for what he simply refers to as “blown insulation”, but he’s making a big mistake: not all “blown insulation” is made of Fiberglass.

Because Fiberglass is made of glass fibers, it itches, but cellulose does not itch in the least, it’s a soft material and is very easy to work with. Once contractors learn the difference between Fiberglass and Cellulose, as well as understand the many benefits of Cellulose, they tend to prefer and strongly recommend it.

“I had blown insulation in my old home and it settled down to nothing..so I don’t want it again”

Here again Fiberglass is the culprit. Much like the cotton-candy that Fiberglass resembles, blown fiberglass becomes fluffed-up when it’s blown into the attic. Over the course of time, blown fiberglass settles and packs tremendously. To be fair, cellulose insulation can also settle over time, but to a far lesser degree. Today’s cellulose is “stabilized” and actually carries a lifetime guarantee to never settle, pack or lose its insulating qualities. So to address the concern, blown Fiberglass absolutely will settle, but not cellulose.  Again, the same mistake of assuming all blown insulation materials are the same.

So why do Insulation companies still use Fiberglass?

1) Most Insulation companies primarily work with new-construction projects that require rolled Fiberglass; the more Fiberglass product they use, the better their purchasing tier and so they tend to promote and use Fiberglass where they can.

2) Blown fiberglass can be “fluffed” and gets amazing coverage, if you can convince customers it’s a good product, it’s much more profitable to work with or you can offer a lower price to get the job.

3) Many companies don’t own the expensive equipment (insulation blowing machine and dedicated truck) to perform the work, so they promote rolled Fiberglass.

4) Most homeowners are very familiar with Fiberglass, they’ve seen it at Home Improvement stores or at new construction sites, so that familiarity lends towards helping sell it.

In all fairness, there are applications where Fiberglass is a prudent choice: under floors where it can be wired in place, on vertical knee-wall sections in an attic or for new-construction and open-framing situations, but with today’s building trends, Cellulose insulation is more often being used because it’s more effective, more efficient, longer-lasting and safer, it’s just a better product.