Many fiberglass installers "fluff" the fiber with extra air,
so you don't get as much insulation as you're supposed to.
This kind of trickery can't easily be done with cellulose, and
certainly not to the extent that it can with fiberglass. (BetterInsulation.com)
Let's look at #5 in more detail.
Houses with cellulose installed burn slower than those with
The Maryland Fire and Rescue Institute (of the
University of Maryland) built three small houses and then
burned them to the ground to see how insulation choice
affected burn time. One house had no insulation, another
had fiberglass, and the third had cellulose. The results? The
house with no insulation and fiberglass insulation collapsed
about the same time, after 40 and 42.5 minutes respectively. The
house with cellulose insulation lasted another 24.5 minutes
longer than the building with fiberglass.
How could this be, when cellulose is made from old
newspaper and fiberglass is made from, well, glass?
The first thing is that cellulose insulation is treated with
fire retardants like borate which make it harder to
burn. But still...how does it outperform
fiberglass? The answer is probably that when you try to
burn cellulose, it chars black but the material is still
there. When you burn fiberglass, it melts away, allowing the
fire to more easily spread. There's a bit in the video
below where someone takes a blowtorch to some cellulose
insulation he's holding in his hand, and the cellulose
won't ignite, it just turns black.
Similar research by the National Research Council of
Canada showed that cellulose insulation increases a
building's fire resistance by 22 to 55% compared to
traditonal fiberglass. (source)
The video below which shows the house-burning test results
was apparently produced by a cellulose company, so we
could assume some bias, but since the test itself was
conducted by the University of Maryland, and since the
fiberglass industry hasn't responded with their own test
showing different results, I think the results of this test
are fairly trustworthy.
However, cellulose doesn't have superior fire performance
in every case. Federal code does say that
cellulose is a fire hazard if it's installed too close to the
sides or on top of recessed light fixtures, or too close to
exhaust flues for things like furnaces and gas water heaters.
And electrical fires are probably more likely in older
homes with substandard wiring when cellulose is installed. (Firehouse
Since cellulose is so common and so important,
its production is regulated by the federal government.
That is, there are minimum standards for quality. It's a crime
to sell cellulose that doesn't meet this standard. (source)
The fiberglass industry
association (NAIMA) snail-mailed me a massive letter
taking issue with this page. I found most of
it to be B.S., but I made a few changes to the article,
mostly minor. Green Building Advisor got a
Sources re: carcinogenity and health effects of fiberglass
"Studies have shown inhaling these fibers can reduce lung
function and cause inflammation in animals and
humans....Fiberglass emits a synthetic material called
styrene, which is a possible carcinogenic according to the
IACR and U.S. Environmental Protection Agency." (Am.