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Fiberglass vs. Cellulose – Insulation Comparison

You’re Ready to Insulate Your Attic, Now What?

Adding insulation to your attic is a great investment in your home. It will go a long way in helping you efficiently regulate the temperature in both winter and summer months. Two of the most popular insulating products on the market are fiberglass and cellulose. These two will most likely be among the options for you when you decide to insulate your home. Let’s take a side by side comparison of both of these products to help you make the right choice for your home.


R-Value is a measure of thermal resistance, or ability of heat transfer from hot to cold through a given material. In other words, the higher the R-Value the better the thermal performance of the insulation. So let’s take a look at Fiberglass and Cellulose in this area.

Cellulose may have a slightly higher R-Value per square inch, but the difference is pretty negligible. The winner in this round – Cellulose

Fire Safety

When choosing an insulating product, you should consider which is going to be safer. A major consideration in this comparison is fire safety.

Cellulose insulation is made from ground up or shredded newspaper which is naturally combustible. In fact, cellulose insulation is regulated as a recognized fire hazard by the Consumer Product Safety Commission. To protect against fire hazards, cellulose insulation is heavily treated with fire-retardant chemicals prior to installation. These chemicals can leach out of the insulation over time. Additionally, smoldering combustion and re-ignition problems are concerns with cellulose insulation should a fire start. Even properly treated cellulose will burn at about 450 degrees. That’s the surface temperature of a 75-watt lightbulb.

Fiberglass insulation is made from sand and other inorganic materials which are melted and then spun into glass fibers. Fiberglass is naturally noncombustible and remains so for the life of the product. It requires no addition fire-retardant treatment.

The clear winner here – Fiberglass


When an insulation settles, the product looses R-Value. If the insulating power is measured by square inch and the product is now not as thick as it was, the R-value has decreased.

Cellulose manufactures agree that their products settle over time. Most set the settling rate at about 20%. When the product is not labeled for installed thickness, the Insulation Contractors Association of America recommends an additional 25% of thickness be added above the labeled settled thickness. That means, you as the customer, pay an additional 25%.

Properly installed fiberglass insulation batts and rolls do not settle. Fiberglass loose-fill insulation will experience minimal settling – less than 1% and will hold its R-Value over time. When the manufacturer’s specifications are followed, fiberglass insulation will maintain it’s thermal performance for the life of the product.

Winner – Fiberglass


Studies conducted in Canada, New England and Ohio demonstrated that wet-spray applications (common application process for Cellulose insulation) do not achieve their advertised R-value until dry. Cellulose insulation may take up to two months to completely dry. In many cases, wet-spray applicaitons may need to remain uncovered until completely dry.

Fiberglass insulation is not absorbent. Under normal conditions all insulation is exposed to humidity in the air. Fiberglass will not wick up and hold water, thus it resists any permanent loss of R-value. In addition, fiberglass insulation does not require a wet-spray application process. This means we never put additional moisture in your attic.

Again the winner is – Fiberglass


As we mentioned earlier, Cellulose requires a fire-retardant treatment. Chemicals routinely used to treat cellulose insulation (particularly the sulfates) can cause corrosion of pipes, wires and fasteners under some conditions.

Fiberglass insulation does not require fire-retardant treatment. It is not corrosive and contains no chemicals that can damage pipes, wires or fasteners.

The winner…you guessed it – Fiberglass

Environmentally Friendly

One of the big claims of cellulose insulation manufactures is their product is more environmentally friendly. Cellulose is generally made up of about 80% recycled newspapers and 20% fire-retardant chemicals. On the surface, cellulose insulation may appear to be the more environmentally acceptable insulation choice as it is made from recycled newspaper. However, it takes three times more cellulose material by weight than fiberglass to insulate a typical home and that has a direct impact on the environment when you factor in increased shipping, transportation and greenhouse gas emissions. In addition an average 1,200 square foot attic insulated to R-38 with cellulose insulation would introduce 300 pounds of fire-retardant chemicals into the home.

The fiberglass industry recycles billions of pounds of pre- and post-consumer glass containers, eliminating the need for millions of cubic feet of landfill space. Many fiberglass insulation manufacturers have plants that use up to 50% or more recycled materials in their products.

While both cellulose and fiberglass insulations are using recycled materials, the lack of chemicals gives the edge to – Fiberglass

Insulating Your Home

When its time to make your home more comfortable, go with the pros. Our goal is never to pressure you into a decision, but rather to educate you on what the right choice is for your home. We use only the highest quality products, and hopefully we’ve shown you why we believe fiberglass insulation is the right choice. If you’d like to get a free estimate to insulate your home, give us a call. We’ll conduct a complete roofing system inspection, including your attic – to make sure your home is properly insulated.


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