Cellulose vs. Fiber Glass Insulation

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When considering insulation for your home, you basically have two choices of insulation: cellulose and fiber glass. What exactly is the difference between these two types of insulation? Which will suit my needs better? Here are some basic comparisons between the two types of insulation.

What it’s made of

Cellulose insulation is composed of primarily shredded newspaper and some chemicals – approximately 20 percent by weight – to reduce its flammability. Fiber glass insulation is made primarily from sand and recycled glass. On average it has 30 percent recycled content, including both pre- and post-consumer content.

Health and Safety

Fiber glass insulation has been tested extensively in studies over the past 50 years. No causal relationship has been linked to exposure to glass fibers and cancer or any other disease in plant workers or installers. With cellulose insulation however, not much is known about its safety. There has been no testing or risk assessment on cellulose insulation. Despite that it is made of primarily shredded newspapers; it does have up to a 20 percent content of chemicals not to mention the paper dust from cellulose insulation.

Fire Resistance

Although cellulose insulation is treated with chemicals to make it fire retardant – those chemicals can fade away over time leaving the highly combustible shredded newspaper behind. Fiber glass insulation being made from primarily recycled glass and sand, both basically non-combustible materials, will not burn therefore not requiring any additional chemicals.

Performance and R-Value

Cellulose insulation stated an R-value but reflect the settled density only. Often times in attics when cellulose insulation is installed at the labeled settled thickness; the homeowner will not receive the state R-value, due to settlement after installation. Usually the homeowner will have to have additional cellulose insulation installed to achieve the stated R-value and maintain thermal performance. Fiber glass batt and loosefill insulations are factory-engineered to retain their thermal performance for a lifetime of the product. When installed properly, they will not significantly sag or settle, insuring that the stated R-Value is maintained.


Cellulose insulation for walls is mixed with water for installation. Vapor retarders are required for cellulose insulation. However, the installer needs to make sure that it is completely dry before closing up the wall cavity. If not, then that moisture can be held in the wall for up to a year. This moisture build up can cause rotting of timbers and corrosion of wires, pipes and other metals in the structure. Fiber glass insulation is made of glass fibers and is not absorbent. The fibers allows water vapors to pass through and it simply drains off. Fiber insulation does not cause any corrosion or damage to the home structure.

Some excellent sources of information for comparing the two types of insulation is the Owens Corning website or speak with a qualified installer. You can also find out more about your region and the recommended amount of insulation for your climate at the Department of Energy’s website.


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8 Comments so far

  1. JaneRadriges - June 13, 2009 at 2:10 pm

    Hi, very nice post. I have been wonder’n bout this issue,so thanks for posting

  2. KattyBlackyard - June 14, 2009 at 11:36 pm

    Hi, gr8 post thanks for posting. Information is useful!

  3. Stuart Ritchie - June 17, 2009 at 8:05 am

    What a load of rubbish. Cellulose is proven by independent studies in Colorado to have better insulating effect than Fibreglass by as much as 25%. It also doesn’t catch fire and does not break down as stated. Studies also show that it Cellulose has better fire resitant properties than fibreglass and will slow a fire down in a home simply because it WILL not catch fire, where fibreglass will melt in a fire and allow the fire to pass through. Get your facts right!!! Cellulose is a better product and a greener product then fibreglass period.

  4. alex - June 17, 2009 at 11:27 am

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  5. Rob Duncan - July 7, 2009 at 8:27 am

    Cellulose and fiberglass insulation do provide a cost-effective means to meet minimal code requirements. But the best insulation I have seen is spray polyurethane foam. It offers superior and consistent R-value AND air sealing, and some types of SPF also provide an integral vapor retarder and add structural strength. Check these products at http://www.sprayfoam.org

  6. cash advance - November 13, 2009 at 12:26 am

    improveit2green.com is very informative. The article is very professionally written. I enjoy reading improveit2green.com every day.

  7. Pete - January 16, 2010 at 10:25 am

    I am an IAQ professional (Industrial Hygienist ). SPF is great insulation but can cause serious sick building issues if not mixed and applied properly (out-gassing of toxic fumes ) . Cellulose is hygroscopic might cause mold problems in high humidity climates if not used with a vapor barrier. I am no great fan of fiberglass but it is well proven and might be the best for all environments considering with respect to mold and outgassing .

  8. solar energy - March 28, 2010 at 12:42 pm

    Have to take pleasure in your energy you add into this blog :)

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