As a rater and insulation contractor I personally respect the overall insulation properties of blown cellulose a lot more than blown fiberglass. I have taken numerous infrared images in attics with the same R-values, both products cellulose and fiberglass. I find time and time again poor performance of blown fiberglass. The R-values are similar, but cellulose is a much denser product.

I was wondering others raters and contractors thought were the same on this topic?

In the area I live in ( Eastern Iowa) there are few contractors are using cellulose, from experience cellulose is a hassle to blow because of the amount dust in the air compared to fiberglass. Is this the same situation in other areas of the county.  I feel that it is worth the dust and dirt because it is denser (giving the customer a better value) and a added bonus is the amount of recycled content in cellulose is a lot greater compared to fiberglass. I feel that there is a lack of education on the topic because most home owners feel that all insulation works the same. I have been working to overcome this idea and promote what I believe is a better overall product.


I look forward to reading any relies on this topic





Energy Core, LLC


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All things being equal & everything being done properly (air sealing, baffles, hatches) - both work fine but cellulose will win out not because of your reasons, but the simple fact that FG R-Value drops the hotter it gets.

Granted you could argue that if it was as dense as cellulose, the convection issue would be diminished but it would not be eliminated & said convection issue is one of the biggest causes of FG's loss of R-Value. Of course once both products are saturated with heat (for better lack of a term) the game is over and it is up to the AC unit to work it's magic  

As an FYI, many FG manufacturers are using recycled materials to make the product & in either case recycled doesn't always mean better - some methods & the means required to make a product from recycled materials can use more energy & put off more by products than simply using new materials

Hi Isaiah, Here in upstate NY we primarily use cellulose for blowing attics and dense packing sidewalls.It's cheaper, heavier, and as you noted performs better in single family residences. The one area that fiberglass works better than cellulose is on mobile home retrofits. On mobile home belly and roof blows it's lighter and absorbs much less water vapor so it's the prefered product.

Oh yeah, I'm a nerd. At big Orange store today and stopped to read Fiberglass blow in package.


And I quote

Another method of insulating your attic is our loosefill insulation. Instead of laying batts or rolls, our AttiCat® Insulation Blowing Machine conditions the AttiCat® Expanding Blown-In PINK® Fiberglas Insulation by fluffing it along the length of the hose, adding millions of the tiny air pockets that give the material its insulating power. Because Fiberglas insulation will not settle, it will maintain the same energy-saving level over time, keeping your home comfortable for years to come.


Mmmm. Fiberglas the maker says will not settle.



My experience with cellulose began when I started to participate in the state of Massachusetts' home energy programs.


Cellulose was mandated for attics and other spaces. Before this, I had only seen blown-in fiberglass in the new home construction industry. Well, I am glad the folks in Massachusetts mandated the use of cellulose.


The material is more eco-friendly, it has proven to have a slower burn rate in tests (compared to all other insulation materials), it can serve as a partial air seal, and the dust issues can be reduced with certain strategies.


Let me also say that I am the foreman\super on all my company's insulation jobs, and I can tell you that (with proper air sealing performed prior to installing loose-fill cellulose insulation) there is no real comparison you can make when it comes to overall effectiveness of cellulose versus fiberglass.


In the end, one cannot stress enough the need to perform thorough air sealing of any space you wish to install blown-in insulation for.

It's Me again. Sorry to swim against the flow but cellulose is a disaster. Dusty, causes allergies, asthma, molds, settles losing R-value, rodents love it, bridges when blown into existing walls, soaks moisture and on and on. Fiber glass is just about as bad and I see fiber glass being the next asbestos. Neither stop air permeation, neither seal any thing, Neither act as a fire barrier both are a waste of money.

Guys, come forth into the 21st century, do your research. Injection foam for existing cavities  and spray foam for open cavities.Telling people that the cellulose and fiber glass is the answer is doing a disservice

Quality foam is the only way to go..   

Given your list of allergies, molds and rodents loving it,  you are not using the cellulose we are discussing.  You are also selling a different product that may or may not be the best for the home owner.

I know everyone sells what is on their shelf.  Not everyone benefits if you only have one product on your shelf.

Up here In Canada Fibreglass wins hands down for heat loss!

Check back 5, 10 & 20 years later on your Cellulous blown attic spaces, in all our inspections the Cellulous had settled 300-400% in all attics, good grief in most cases we could see the top truss cord, that's R12 or less!

All insulations work due to air entrapment and once settled all insulation has reduced properties.

WE are currently re-blowing many attics using the new pink, which doesn’t settle due to moisture or any other reason is 100% recycled and dust free and does a much better job of entrapping air and keeping those air pockets for the life of the insulation. 

This December from the outside using a heat loss gun check both attics, and a few older jobs you will get the picture.

Hi Isaiah,

I have experience with both fiberglass and cellulose. I think that cellulose is better.   Dr. Energy Saver on has a video to explain the differences.  See info below.

Why Cellulose Insulation is Better than Fiberglass Insulation    See  video on Dr. Energy Saver 
On episode 50 of the "On The Job" web series, Larry Janesky, owner and founder of Dr. Energy Saver, demonstrates how different types of insulation materials perform when exposed to fire.

In Episode 51, he continues to compare insulation materials, by showing the differences in performance of two types of materials commonly used in attic and wall cavity insulation: fiberglass and cellulose.  Fiberglass insulation is frequently used in the United States, but as this video will show, cellulose insulation outperforms fiberglass in the vast majority of applications.

Cellulose insulation is entirely made of recycled paper: old newspapers, phone books, and paper stock. To make that shredded paper suitable as an insulation material, the cellulose is treated with environmentally-friendly chemicals. In its original state, cellulose is very attractive to insects and known to support mold growth. Boric acid, a harmless chemical used for decades in many household applications as an antiseptic and insect repellent, is used to deter pests and prevent mold growth.

Also since paper is highly flammable, cellulose insulation is treated with a fire-retardant material, making it outperform most types of insulation materials, including fiberglass, in terms of fire resistance.

Using a little display built to compare cellulose and fiberglass, Larry shows how quickly and easily heat passes through a layer of fiberglass insulation when compared to a layer of cellulose insulation. Cellulose is denser than fiberglass and that gives the material a better R-value and makes it better at preventing heat transfer.    That kind of performance makes all the difference during hot summer months when you are trying to keep the scorching heat from the attic from getting into your living space, or during cold days when you are trying to keep the heat from the conditioned area from being transferred to the freezing cold attic.

Keep drinking the cool aid

Chris, to what are you referring to as the Kool Aid?

If you are referring to cellulose then I suggest you get out in the field and blow a few attics with the best loose-fill fiberglass (something like OC L77) and cellulose (something like National Fiber CEL-PAK). Test the results and tell me how you feel (physically) after working with each.

I and many others know what we are talking about, and not because some study or some Doc told us (not to disparage Dr. Energy Saver). Fiberglass has its place...I use FG batts in quite a few applications, but I ardently feel that loose-fill FG is simply inferior to loose-fill cellulose.

This discussion is honestly a waste of all our time. Seal up your building components well and then it really doesn't matter what you insulate with as long as it's done right. 

P.S. I took my 1904 bungalow, sucked out all the old nasty formaldehyde-ridden insulation and debris, and went for what I believed would be a cost-effective solution for decades to come. Knauf EcoBatt insulation in the walls and in the attic, closed-cell spray foam for air leakage locations, and foil-faced polyiso board on top of the wall sheathing. I still do not have heat in my house, and plan to forgo AC. I am pretty darn comfortable now, and was so throughout most of the summer in Arlington, VA.

My point: I am not "sold" on any product or technique, but am rather convinced that a portfolio of products and techniques combined with intelligent design get the job done. Any issues with this line of thinking?


The Cold Climate Housing Research Center in Fairbanks, AK has alot of information about this topic.

Great site for those living in Alaska and building on Permafrost.


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