Inspector, Steve Medina, compares between blown cellulose and fiberglass insulation for fire safety, efficiency, price, and lifespan. 5-15-2010  

  Part 1  

Part 2  

 Summer is practically here and temperatures are rising fast. On the way to work in the mornings, you''ll be bombarded with energy efficiency commercials telling you to "buy now before our specials are over"! They'll tell you that rebates and tax credits are abundant and that you'd be a fool not to save money on your utility bills. If you're considering installing more or new insulation in your attic, why not choose the right product that gives you value for your money.

Blown insulation is very popular right now, because it costs less, and is easier and faster to install compared to the batt type. Blown cellulose and fiberglass are currently the most prevalent at the supply houses and among contractors, so I took it upon myself to visit the two obvious largest home improvement stores to compare pricing, availability, and quality. The packaging on the cellulose insulation jumped out at me with "green" words and colors, and claiming 85% recycled paper. The fiberglass packaging didn't have similar colors or say much except for the R value rating and name brand. What most people don't realize is that almost every product manufactured and sold is recycled, infact, fiberglass insulation is 40% recycled glass.

After taking notes and picking up some samples, I headed home to perform some tests and play devil's advocate. I took a video for the public to see and judge for yourselves. Below are my conclusions:

Hypothetical model: To install new insulation for 1000 sq ft attic space to achieve R-38 value.

Efficiency: Cellulose, aka, recycled paper has a per inch R Value of 3.7 per inch of thickness. Fiberglass has less of an R Value of 2.5 per inch. Less inches of cellulose is required (10.5 inches) than fiberglass (14.5 inches) to achieve an R-38 value. However, because of a two inch settlement factor for cellulose, to achieve 10.5 inches, an extra 2 inches needs to be blown making it 12.5 inches.

Cost: The two blown materials come in bales or bags, but differ in amounts of square footage they fill per bag. Each cellulose bag costs $11 and requires 60 of them to achieve 10.5 inches (R-30) at an approximate cost of $780. Fiberglass bags are $26 per bag, but require only 20 bags to achieve 14.5 inches at a cost of $540. Fiberglass costs less.

Lifespan: Insulation needs to last a long time by staying fluffy, clean, and dry. Central Texas is very humid and insulation must withstand absorption over the years to keep it's thickness. In my test, I took two samples of insulation and poured 1/2 inch of water over them to see if they would absorb and flatten. The fiberglass insulation repelled the water and kept it's composure, but the cellulose absorbed it and lost an inch of thickness.

Safety:  Fiberglass insulation is considered hazardous during installation because of the fibers' ability to be breathed in without protection of a filter mask. In a flame test, I took a lighter and attempted to light the fiberglass, but it would not lite, nor smolder. The cellulose smoldered and charred, but would not stay on. Cellulose is sprayed with an anti-fire chemical, but I'm still wary if a certain batch out of the manufacturer may not be sprayed correctly. I'm also wary of cellulose paper covering wiring and recessed lighting.  

Conclusion: There are other types of insulation such as rock wool, foam, pellet, etc etc. Out of these two I prefer the fiberglass for obvious reasons, but prefer the batt or rolled type. 


P.S For a better understanding, watch the video above. This is my first video, they'll get better with time.