Blown in Fiberglass Insulation Vs. Cellulose Insulation

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There has been a debate going on for years over the best insulation for homes. Fiberglass insulation has definitely been around the longest, but in recent years, blown-in cellulose has become increasingly popular. The cost of each is about the same, but each has advantages and disadvantages. Choosing between fiberglass insulation and blown-in cellulose insulation is a big decision for new home construction, and several issues must be considered.

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How Insulation Is Made

Blow-in cellulose insulation is made from shredded newspaper with chemicals added to make it fire resistant. Manufacturers use about 75 percent recycled materials, which makes cellulose insulation environmentally friendly. Fiberglass is made by blowing molten glass through very small heated holes to create long strands that are then matted together to form the insulation. Fiberglass insulation is made up of about 25 percent recycled materials.


Blown-in cellulose is thinner than fiberglass insulation and it fills the space easily, while fiberglass has to be cut to fit spaces and physically put in place. Blown-in cellulose will surround pipes and other objects easily, while fiberglass leaves gaps and only goes where placed..


Blown-in cellulose is treated with chemicals to make it less flammable, If there is a fire, it can slow the fire down and actually create a fire wall. When it does burn, it does not emit toxic chemicals. Fiberglass is hard to ignite, but once it gets started, it burns fast and emits toxic chemicals.


Cellulose insulation requires a blower for installation that can be rented from your local home improvement store. The insulation easily blows around obstacles and fills odd-shaped cavities, but it's mixed with water and can take up to one year to completely dry. Fiberglass must be cut to fit around objects and physically put in place, which is a time-consuming process and not usually done completely. Fiberglass must be installed with protective clothing because the fibers can cut the skin.

Air Filtration

Blown-in cellulose insulation is two to three times denser than fiberglass insulation. Scientific studies have shown that cellulose reduces air infiltration and saves considerable energy compared to fiberglass insulation.


Blown-in cellulose is more moisture resistant in the long run because of its chemical content, but because it's mixed with water when installed, there's that long drying process. Fiberglass allows moisture to pass through its fibers, but if water leaks through the wall with no drainage, it will adsorb the moisture, which will cause gaps in the insulation and allow heat to escape from your house. When this occurs, the R-value decreases and heating costs increase.


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