Ever had anyone invite you to check out his or her new fiberglass long underwear? We haven’t either!

The following is an effort to share what we have learned. It is fact based, which is to say we have made a grievous attempt to remove any/all bias. As ever, there is no need to take our word for it, thus we hope this inspires continued individual research, if nothing else.


Fiberglass is the dominant player in the industry. Reports vary but one would be relatively safe suggesting it occupies considerably more than half of the overall market. Though it shrugged the carcinogen label in 2011 you might want to bone up on your understanding of biopersistance versus biosolubility before making a buying decision. Anecdotal evidence suggests that industry participants would be more than happy to never see or touch the stuff again. There are two articles below that explain the evolution of its label. They may or may not have a bias!

Mercola Article

North American Insulation Manufacturers Associate Article


Cellulose insulation is recycled newspaper. Is paper an insulator? Installed properly cellulose possesses positive resistance to thermal conductivity. That is, its R values are good. However, it is paper. What happens when paper gets wet? It smells and produces mold. What happens when paper catches on fire? It burns quickly. How does one resist fire? A shed load of chemicals. We don’t know an installer that would put this product in their own home; we have ‘saved’ a few homeowners that were overwhelmed by the dust caused from cellulose insulation, and we recently hear that a shortage in newspaper may be allowing for garbage to be mixed in as ‘filler’.

UMASS liked it 10 years ago

A more recent, and quite common story concerning cellulose


Foam insulation comes in all shapes and sizes. There is rigid board, and open and closed cell spray foam – to name a few. The foams are all different and no one understands their true consistency on either an absolute or relative basis. In other words, the manufacturers don’t want to reveal their IP and because the chemicals are sourced around the world there is no way of knowing what is really in each barrel. We understand that BASF will guarantee 99% consistency, but it comes at a price that often leads the installers back to the ‘other guy’.

Inconsistencies in the raw materials notwithstanding, the problems purport to be much more grave at the install level. For fun, let’s just assume the chemicals are indeed delivered uniformly. Now consider the variance in spray mechanisms. Different nozzles mix at different rates. How does an installer choose which nozzle to use and do they switch appropriately? Now consider a live application. You don’t have to be a chemist to understand mixing rates vary outside of a controlled environment. Assume you start the job at 8am and it is 50 degrees. What happens at 3pm when it is 77 degrees and your installer is spraying the same way? Are you getting the same R value? Are you getting cavities with a consistent mix of chemicals? Is one space likely to off-gas more than another? What if the answer is yes and that space is your kid’s bedroom? Answer: no one has a clue. A whole other set of considerations when things go wrong: who’s fault is it? Same answer!

There are a boatload of questions that seem to be entirely unanswerable as it relates to foam insulation. One thing we do know is that roughly one full dumpster of shavings are sent to landfill from a job site of any size. How long does it take for those particles to add to the 46,000 bits of plastic per square mile in the ocean? Ask Google and any/all industry participants for an opinion before making any decisions here.

Mineral Wool

Mineral wool is a mixture of basalt rock and slag. It is generally known to be a fairly reliable product. It may, however, carry the highest net embodied energy in the industry as it relates to production. Extreme heat is necessary to melt the slag which allows for a bond with the rock element. We understand formaldehyde is used as a bonding agent; it is said to burn off leaving only trace elements. Formaldehyde is a carcinogen and some will not touch ‘rock wool’ as a result.


Recycled blue jeans are a nice effort. However, there are inherent weaknesses in a cotton fiber. It burns, breaks down when wet and is conducive to mold growth. A new home for old blue jeans is a nice idea, though it unfortunately does not usurp the reality that, as a fiber, cotton sucks.


Wool is a high-integrity fiber that has evolved over thousands of years so as to protect sheep from the elements. It is renewable and sustainable, a great insulator – boasting some of the higher r-values per inch in the industry, save foam, and compostable at the end of an extended useful life. It manages moisture against 65% relative humidity and irreversibly bonds with formaldehyde, NOx and SO2. The wool trade is also responsible for the sequestration of some 525,000 tons of atmosphere-derived carbon.

Think about it this way. If you are going skiing or hiking and have the option to wear fiberglass, newspaper, foam, steel (slag), cotton or wool which would you choose?

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