Fiberglass vs Cellulose

Good information for those interested.

Good one Thanks … Roy

I usually see fiberglass batts with blown cellulose on top.

One would think the fiberglass is less likely to contain mold between the two just because it is made of glass vs organic paper products.
Guessing the air space traps debris it feeds on.
Certainly would rather have batt than loose fill in a wall if you might be working there some day.

Putting the cellulose on top of the fiberglass is usually done in an attempt to use the air sealing properties of the cellulose. The problem is to get it’s air sealing benefit it really needs to be against the drywall and the framing since the fiberglass is so air permeable and there is no way to blow over it and seal all sides. If you want to keep the batts they need to be pulled back and then replaced after air sealing. You can then blow more fiberglass on top.

The cellulose has a chemical in it to prevent mold growth, termite damage and a fire retardant.

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This website has the correct information about celloulse

Cellulose is not an air barrier. I am actually not sure why someone would install cellulose on fiberglass. As you compress fiberglass it loses its R value.

Dense pack cellulose is the best retrofit product for walls. One thing I didnt see kn the GBA article is how most fiberglass is installed improperly, which makes cellulose a better product in the long run.

Most people do not realize there are different qualities of cellulose. The real deal is more expensive but covers better and insulates better.


Cellulose does slow air movement and I do see that reflected in houses I test. I did not say it was an air barrier.

I like to explain to homeowners that fibreglass always has seams when installed (even when cross layed) and cellulose creates a continuous “blanket” of insulation with no seams. They seem to understand a bit better then.

Interesting subject area that may become very important in the future.

What are you doing up so early Bob?

What are you doing up so early linas?
Don’t answer as i am sure you will brag about having some 6:00 am inspection.

In my case I am working on a project and not inspecting today.
i average 3 full H.I a week in March.

But I am honest so do not bother answering.

I’m flying down to North Carolina to join Jefferey’s snake worshiping cult. Wish me luck.

Somehow I have no doubt you are being honest.
Eye yi eye.

Somehow I become convinced you are actually Danny Devito and every day is sunny in Pil…

It really does end up being like a blanket when it’s dense. You can almost pick it up. With it’s dust and being so much heavier than blown fiberglass I rarely see it more than 5 inches thick here.

Look also here:

Thanks Jim… Your’s did not work for me try this … Roy

Down load Book 22 pages

Not all Cellulose has that property contained within
Only TAP Insulation

Come on down Linas, I sure I can find a copperhead around here… I will even teach you a thing or two about cellulose which I have been installing in the homes I build for over 20 years.

Cellulose is a great product…price is comparable but the effectiveness is so much greater. The first home I built for myself was just over 2000 sq ft. and insulated with fiberglass. The 2nd home was over 4000 sq ft, ceilings ranged from 9 ft up to 20 ft and I used cellulose…it cost me the same to heat the 4000 sq ft then it did the 2000 sq ft. After that I was sold on the product and have not looked back since.

The only problem I had was with dry wall crews not being careful…knocking out the cellulose creating cavities… I finally had my installer simply put up netting wherever it was going to be installed on vertical walls and that took care of the problem.

Not true…Applegate has been doing it for 20 years…that is what I have used. They actually started out as HVAC contractors in the early 50’s…great company…and got into cellulose insulation the 70’s.