Showdown: Blown Cellulose v. Fiberglass Batts

Comparison of Fiberglass and Cellulose Insulation

We’ve come to realize our blog and website have become a reference for many homeowners and pest control companies alike. One of the most perplexing questions to answer after you’ve had your attic cleaned, and your insulation removed, is what type of insulation to install. Whichever product you choose will remain in your attic for over 20 years, hopefully up to 40 years as long as it’s not disturbed. With this in mind we feel it warrants a little exploration. The purpose of insulation is to prevent heat transfer. In other words, insulation in the attic is meant to keep heat inside the home in the winter or heat outside the home in the summer. You can understand how important insulation is when you think about how uncomfortably hot or cold your house can be during different seasons of the year.

The first and biggest difference is what the two types of insulation are composed of. Cellulose insulation is made from 75-85 percent recycled newspaper, the rest of the volume by weight are chemicals used to make the newspaper non-flammable. The newspaper is shredded and treated with the chemicals to make the product that’s blown into your attic. Fiberglass insulation is made from sand, sodium carbonate, and limestone, which altogether make a glass. The recycled glass material is heated into a molten state and jetted through tiny heated holes into high speed air streams. This process creates extremely long fibers which are matted together to make the batts which are pressure fit installed into your attic. Round 1 is a tie in my book.

Onto which is a better performer. After both types of insulation are installed at an equal R-Value cellulose insulation will be 2-3 inches lower than fiberglass insulation. Most importantly the performance depends on the quality of workmanship. Lastly, cellulose insulation is able to flow into every crack and crevice where installed, fiberglass is stationary wherever installed. Because of cellulose’s ability to potentially cover more area than fiberglass I give this round to cellulose.

As mentioned, cellulose is treated with chemicals for fire resistance. Blown cellulose insulation can slow the spread of fire and create a 2-hour firewall. Fiberglass is naturally inert which makes it extremely difficult to ignite. However, once it is ignited it can burn fast, hot, and could emit toxic gases. We’ve removed both burned cellulose and fiberglass insulation and I’ve found the fiberglass is more intact than cellulose after burned on average. Since cellulose is made of materials highly susceptible to igniting I give round three to fiberglass.

Hands down installing blown cellulose insulation is easier than installing fiberglass batts. Fiberglass is itchy, you need to get to every place in the attic where it is to be installed, and the bags can get heavy. You can blow cellulose insulation from a few feet away, its not irritating, and you only need to carry around a light weight hose while installing it in the attic. In extremely tight attics blown cellulose is sometimes the only option available for homeowners. Cellulose wins again.

Lastly, a major issue that needs consideration with insulation is moisture resistance. For blown cellulose insulation a moisture barrier is a must in humid climates. Cellulose can retain moisture for over a year, which could subsequently lead to mold. Fiberglass insulation allows for water vapor to pass through it. However, if water were to leak through your roof or wall the fiberglass may absorb the moisture and cause sags or gaps of insulation with no drainage, which would result in heat escaping or allowing heat into your house. With the fact that cellulose can retain water longer than fiberglass the last round goes to fiberglass.

Wow, a split decision, that leads us nowhere! From what I’ve found, choosing the type of insulation you will install in your home comes down to two things. The first is your previous experience with one type of insulation or the other, the second is whether or not you have plans to remodel or work in the attic in the future. Many people have had bad experiences with blown type of insulation. It’s messy, ugly, and difficult to work with after installed. If you have plans to remodel any part of the home with an attic over it, install can or recessed lights, upgrade your hvac system, or perform any work in the attic, fiberglass is much easier to move and put back in place than cellulose is. Making it a much better option if you have any projects in mind. Otherwise, you can opt for a more efficient type of insulation in cellulose.

I hope this helps on your way to a clean attic.

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