Cellulose or Fiberglass Insulation, Which is Better for Your Attic?

Choosing the right material for your home’s attic insulation can have a lasting impact on your comfort as well as your heating and cooling bills. Prior to choosing an insulation material, it’s important to understand the properties of your attic insulation.

At Dr. Energy Saver and Attic Systems, we prefer blown-in cellulose over blown-in and fiberglass batts for several reasons:

 Cellulose insulation versus fiberglass batt insulation


R-value measures the resistance of heat flow through a material – the higher the R-value, the better the material is at resisting heat flow. In most situations, we prefer the air and heat flow resistance of cellulose over that of fiberglass. At 3.5 per inch of material, the R-value of blown-in cellulose is 23% better per inch than fiberglass batts!

According to research done at the Oak Ridge National Lab, fiberglass loses up to 50% of its R-value in very cold conditions; making cellulose a better choice for homes in northern climates. In the summer, according to research by the Brookhaven National Lab, fiberglass loses 3 times more R-value than cellulose when attics reach 110 degrees (F) – very common in most areas of the country.

Dr. Energy Saver and Attic Systems contractors blow in cellulose up to a depth of 17 inches (R-60), completely covering the wood floor joists, which have a low R-value and can transfer heat to and from the attic and home. Fiberglass batts are placed between floor joists, allowing for greater heat loss as air moves through the wood joists

Air leakage

Air leakage through cracks, voids, and gaps in your home insulation is responsible for approximately one-third of an average home’s heat loss. Heat and comfort are also lost through convection; when drafty currents of air within the house, wall cavities or attics, move heat to other locations.

Since cellulose is blown in, it fills all the gaps, crevices, nooks and crannies in your attic, unlike batts that can leave gaps. Compared to fiberglass, cellulose is a superb air-blocker.


Air moving through a vented attic deposits dirt and dust into fiberglass batts; this is called wind-washing.  Dirty fiberglass batts have a significantly reduced R-value.   

Because it is denser than fiberglass, cellulose is much more resistant to wind-washing.

Cellulose is “Green”

Cellulose is made of 80% post-consumer recycled newsprint. The Cellulose Insulation Manufacturers Association (CIMA) claims that insulating a 1500 square foot house with cellulose will recycle as much newspaper as an individual will consume in 40 years. If all new homes were insulated with cellulose, this would remove 3.2 million tons of newsprint from the nation’s waste stream each year.

Cellulose is treated with borate minerals that prevent insects and rodents from eating the material. It also will not rot, decay or mildew, and cellulose does not support fungus or mold growth.

Cellulose and moisture

Wet insulation of any type is bad. But cellulose is hygroscopic, meaning any moisture it encounters is dispersed throughout the material. This prevents liquid from accumulating in any one area. Cellulose can help dry out other materials in contact with it and does not support mold growth.

Cellulose insulation is safe.

Although cellulose is made of paper, thorough mineral treatment provides it with permanent fire resistance. Unlike fiberglass batts with paper backing, it doesn’t burn as you might expect ground up paper to. Despite competing industries stating otherwise, independent testing confirms that cellulose is safe and approved in all building codes. In fact, many professionals consider cellulose to be more fire-safe than fiberglass. This claim rests on the fact that cellulose fibers are more tightly packed, effectively choking wall cavities of combustion air, preventing the spread of fire through framing cavities. (Check out this YouTube video: The Big Burn).

To learn more about the many benefits of cellulose insulation, contact your local Dr. Energy Saver dealer today to schedule your estimate.

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