Blown in Insulation- Fiberglass or Cellulose?

by Murray Anderson

Have you ever noticed that things you think should be simple and straightforward often aren't? You'd think after you made the decision to add some blown insulation into your wall or attic, the hard part would be done, I mean insulation is insulation isn't it? Actually, the answer is no, cellulose and fiberglass are the tow most popular types of blown insulation, and they each have some pros and cons, so, depending on who you talk to, you'll get different recommendations. Here's some details on the differences between cellulose and fiberglass insulation.

Insulating values

Both cellulose and fiberglass have similar insulating values although cellulose does have a slightly higher R factor (cellulose has an R-value of approximately 3.0 per inch while fiberglass ranges from R-2.1 to R-2.7). However cellulose will settle over time potentially leaving some areas (in wall particularly) with little or no insulation. Fiberglass manufacturers have developed blown fiberglass insulation they claim won't settle over time.
Cellulose retains its insulating value no matter what the temperature, however, fiberglass has been shown to lose some of its insulating value as the temperature drops. In extreme temperatures the loss of insulating value can be as much as 50%.

Health concerns

Loose fill or blown cellulose insulation is manufactured primarily from recycled newspapers, a very benign product so it poses virtually no ongoing health risk.
Blown fiberglass on the other hand is made up of very fine strands of glass and the tiny fibers may be considered a carcinogen since the fibers can easily be inhaled into your lungs. The offset to this potential health concern is that once fiberglass insulation is installed, it is usually covered with something or it's installed in an area where it won't be disturbed (such as an attic) so the fibers won't get into the air where they could be inhaled. In fact in a letter to Congress the U.S. Department of Health Human Services stated they don't believe fiberglass insulation is a threat to people in their daily lives.

Safety concerns

Since cellulose is made from newspaper it obviously will burn. Cellulose insulation manufacturers have responded to that concern by treating the cellulose with fire retarding chemicals such as boric acid, ammonium sulfate or sodium borate in the manufacturing process. These chemicals have the additional benefit of repelling mice and other rodents. How well the fire retarding chemicals work depends on the manufacturer's quality control during the manufacturing process.
Fiberglass on the other hand because it's made from glass simply won't burn (although it will melt I extremely high temperatures).

Other factors

Cellulose contains the higher percentage of recycled materials. While the fiberglass industry does a good job of recycling and uses approximately 35% of recycled material, cellulose manufacturers average over 75% of recycled content.

Conclusion

Fiberglass insulation has proven over the years to provide effective temperature and sound insulation while more recently, cellulose has established itself as a viable alternative. Since either will do an effective job insulating your home, the insulation you choose should be based on other factors such as cost and availability of the product, quality and reputation of the installers (if you're not doing it yourself) and your personal environmental concerns.