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

Comparing cellulose vs fiberglass insulation 

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. No matter what type of insulation you're considering, whether it's fiberglass batts, blown-in fiberglass, cellulose insulation, or another material, weighing the options and deciding on the best insulation for your home starts with understanding the properties of each insulation material. In this blog, we'll discuss the benefits of cellulose over fiberglass and why it might be considered the better insulation option for insulating attics.

 

R-Value

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.

Wind-washing resistance

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.

Sustainability

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 yearly waste stream.

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.

Moisture and mold resistance

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.

Flammability

Although cellulose is made of paper, thorough mineral treatment provides permanent fire resistance. Unlike fiberglass batts with paper backing, they don’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. 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 and preventing the spread of fire through framing cavities..

Installation: Choosing the right contractor

Finding the right contractor to install your attic insulation is just as important as choosing the right type of insulation. Dr. Energy Saver not only offers high-quality materials, but attic insulation is installed by trained professionals who can educate you about the benefits of cellulose insulation and help you make an informed choice.

Contact your local Dr. Energy Saver dealer today to request a free estimate for home insulation services.

Updated on January 31, 2025