Common Insulation Materials

A focus on existing homes

Article take-away

The focus of this article is on blown in cellulose insulation, blow-in fiberglass and fiberglass batt insulation because these are the product we find in 99% of homes we inspect. In most cases, when our estimators inspect attics we are much more concerned about the quality of the material “installation” than the types of insulation materials in the attic. We know that the materials commonly used in existing homes can be undermined by poor installation. At Advantage Home Performance, we blow both cellulose and fiberglass insulation into attics and we think the research bears out that they are both good insulating materials.

Why the confusion surrounding different insulation materials

At Advantage Home Performance we know from firsthand experience that there are a lot of people with strong opinions about insulation the marketplace. We believe that many of the manufacturers and sale people who are sowing confusion in the marketplace are more interested in market share than they are an honest discussion about the pros and cons of different materials. In this article we will do our best to be objective in our discussion regarding insulation materials.

This article is mostly focused on blown in cellulose and fiberglass insulation. These are the materials we find in more than ninety-nine percent of the existing homes we inspect. If you are interested in learning more about spray foam, we have an article on spray foam insulation that covers spray foam material properties.

Quality installation is more important than material type

In our retrofit business we take a much stronger stance on quality of installation than we do on product type. We know that the materials commonly used in existing homes can be undermined by poor installation. We also know that small thermal defects can have a huge impact on R-value. This is why quality of installation is often more important than the type of material being installed.

The impact of missing insulation in an attic is surprising. A home that is missing 5% of the attic insulation (bare sheetrock) will see a resulting drop in R-value of 54%. R-value measures resistance to heat flow – the greater the R-value, the greater the insulating power.

Here are two common examples to illustrate my point. In the photos below you can see the blown-in cellulose taper down to bare sheet rock. This is an installation and supervision problem and not a insulation material problem. The photo on the right is a knee wall, a wall between the house and attic. which was never insulated. You can see the bear sheet rock.

In both these cases it does not really matter what type of insulation was installed, be it blown-in cellulose, blown-in fiberglass or batts. The insulation material itself is the not the problem. The “installation of the material” is the issue and not the material. The whole argument about what material is a distraction.

Common insulation materials

You’ll find three commonly used types of insulation in attics: blown-in cellulose, blown-in fiberglass, and fiberglass batts. Although we see rock wool in older homes, we assume it has been a couple of decades since rock wool has been blown in attics in Arizona.

Per 1”
Blown Cellulose3.6 – 3.810”Typically grey
Blown Fiberglass2.5 – 3.013” – 15”Pink, yellow or white
Rock Wool2.515”Greenish brown, black
Fiberglass Batts3.1 – 3.712”Common colors are pink & yellow

* R-value measures resistance to heat flow – the greater the R-value, the greater the insulating power.

Blown-in cellulose insulation

Blown cellulose is a grey insulation material commonly blown in Arizona attics. “The word cellulose comes from the French word for living cellule and glucose, which is sugar.” Cellulose is the structural component of the primary cell wall of green plants. For industrial use, cellulose is primarily obtained from wood pulp and cotton. It is mainly used to produce cardboard and paper.

Cellulose insulation is 75%-85% recycled paper, usually post-consumer waste and for this reason is a favorite of the green movement. The remaining percentage is the fire retardant which is either boric acid or ammonium sulfate or a blend of the two.

Cellulose has an R-value of 3.7 per inch. It will settle when installed in attics and if installed correctly this settling is factored into the installation. For instance depending on whose product we are blowing, the coverage chart will call for an additional 15% – 20% to account for settling. For example we’ll blow 9.8″ of cellulose, which we know will settle to 8″ or about 15% to 20%.

In many of our customer’s eyes, cellulose insulation biggest virtue is that it does cost less to blow an attic with blown-in cellulose insulation than blown in fiberglass.

Blown-in fiberglass insulation

Blown fiberglass comes in three common colors: white, pink or yellow and the colors simply identify the manufacturer. Blown-in fiberglass insulation in attics typically has an R-value of 2.5 per inch. The density of the blown-in fiberglass determines the R-value just like it does for a batt. This is why we can purchase a 3.5” batt with R-values of 11, 13, and 15.

A newer white blown-in fiberglass
An older yellow blown-in fiberglass

Fiberglass insulation is manufactured from silica. Silica is most commonly found in nature as sand and quartz. The silica is melted and then spun into a glass fiber which is used in the manufacture of fiberglass batts and blowing wool. The fibers trap air and that is how the R-value is derived.

The older versions of blown-in fiberglass were itchy and often would make our estimators cough during attic inspections. Today the material has evolved remarkably. Some of the blown fiberglass insulation products feel more like a cotton fiber than a glass fiber.

In the past there was a concern that some blown fiberglass could be fluffed; i.e. whipping the blown fiberglass up with air, which compromises density and thus R-value. Based on limited experience performing core sampling we don’t believe fluffing is a problem in Arizona.

Fiberglass batt insulation

Fiberglass batt insulation typically comes in pieces the width of the stud or truss bays. The problem with fiberglass batts is they are installed by people who are rewarded for the quantity and not quality of installation. The R-value of fiberglass batts can be easily undermined by sloppy installation. Most insulation company’s piece rates are not high enough, so all of the focus is on production.

A fiberglass batt being installed in an attic
A fiberglass batt being installed in an attic

Health and safety issues surrounding cellulose and fiberglass insulation

Advantage Home Performance is committed to installing quality products in a safe manner. With the exception of the kraft faced paper on some fiberglass batts when installed in the wrong areas, we do not believe that the blown in cellulose and fiberglass will compromise the health, safety, and or value of your home.

In the battle for market share some manufactures will try to convince you that cellulose insulation is a fire hazard and that fiberglass insulation is a carcinogen. Our thorough review of existing research dispels these myths. If indeed these myths were substantiated with facts, trial lawyers would have put these industries out of business a long time ago.

In regard to fire safety, the only insulation material we are truly concerned about is kraft paper on some fiberglass batts. The paper on kraft faced batts can pose a risk, if installed against, chimney, flue pipes and some recessed light fixtures. We take extra care to train our installers how to safely install kraft faced batts.

Rock wool

To the best of our knowledge blown-in rock wool insulation products are no longer being installed in the Arizona. Since we do occasionally come across these two products in much older homes, we decided to provide a brief description of both materials.

Light green colored rock wool insulation Charcoal colored rock wool insulation
Light green colored rock wool insulation
Charcoal colored rock wool insulation
Charcoal colored rock wool insulation

We come across blown-in rock wool insulation products in houses built in the 60’s and 70s. Based on our numerous trips into existing homes, we suspect blown-in rock wool insulation has not been blown in attics in Arizona with any frequency since the late 70’s. We have seen green and black rock wool Arizona. The R-value of blown-in rock wool ranges between R-2 and R-3 per inch.


Every once and a while we run into an older houses built in the 50’s or earlier that have poured in vermiculite insulation. Vermiculite is a naturally occurring mineral. “It has the unusual property of expanding into a worm like accordion shaped pieces when heated. The expanded vermiculite is a light-weight, fire resistant, absorbent, and odorless material.” There is the potential for some vermiculite to be contaminated by asbestos. We encourage you to visit the EPA website and do a search on vermiculite, if you have vermiculite in your attic.

Make the most out of your home's insulation

Get quality installation