I am planning to add blown-in cellulose (GreenFiber) to my 15' x 40' attic, which currently has blown-in pink (circa 1971) which has really settled/compacted. A lot of it, I can actually pick up in sheets and/or good-sized chunks. If I stuff some into trash bags, can I dump it into the blower I get free from the big box store when I buy the cellulose and re-blow and re-fluff the fiberglass before I add the cellulose? The Cocoon machine at Lowe's has a warning label about only using cellulose, user assumes liability, etc.

  • 1
    When you cut open a new block of cellulose it will rapidly expand (seriously don't cut it open to test this theory you'll never get it into the machine) Point is I don't know if increased density will cause problems for the machine or not...safest bet would be to just blow over the top of the old stuff.
    – James
    Commented Jul 29, 2014 at 20:21
  • 1
    The machine says to only use cellulose for a reason, and if there are adverse consequences it will be pretty obvious that fiberglass was fed into it. Basically this is picking up nickles in front of a steam-roller - there are much more productive home improvements than reblowing the fiberglass - e.g. installing radiant barriers, insulating ductwork, sealing around openings, etc.
    – user23752
    Commented Jul 30, 2014 at 12:19
  • Possibly the fiberglass was bonded sheets originally and not loose wool?
    – Wirewrap
    Commented May 30, 2022 at 14:47

4 Answers 4


Whether you can or not, you probably don't want to. If you're going to go through the trouble trouble of pulling out the fiberglass, you might as well just replace it with cellulose, which has a significantly higher R-value (around 50% higher per inch than fresh loose fill fiberglass). Your settled fiberglass, on the other hand, has a significantly higher R-value per inch than the fresh fluffy stuff! The settling of loose fill insulation is only a problem because you lose inches faster than the R-value per inch increases. "Fluffing" what you have now would save you a little bit of cellulose but if you still fill to the same depth, but would leave you less insulated.


The more you compress insulation the more the R value goes out the window. You should expect some settling but you shouldnt be pulling it out in chunks or sheets. I agree with Zhentar on pulling the old insulation as it is adding weight to your drywall ceiling (and you may not want to add to it) plus compacted that much it is not earning its keep. As far as pulling it out in sheets / chunks you should really check / recalculate your ventilation. settling is normal but chunks and sheets ar an indicator of high moisture content. As far as loading it into the machine.... the auger should have a grate above it that the bag can rest on. Make use of it. set the bag on the grates and cut the bottom. Itll feed the machine instead of your front yard. Best of Luck !


Fiberglass has a settle rate of ZERO! These guys are just completely wrong. Cellulose has a significant settle rate which is why all cellulose manufactures recommend blowing more insulation to compensate for the settle. All loose fill fiberglass companies list ZERO settlement. The only time fiberglass will settle is if there is a moisture issue. Either from the home or from the roof or ventilation. And a qualified insulation contractor will advise of that with sealing of penetrations, adding more exhaust roof vents or equalizing the ratio between soffit to roof vents. Cellulose will settle regardless as it is made of recycled newspaper. And anyone that has left a paper on the driveway knows what happens...it shrinks. You have probably already solved your issues, but my recommendation also follows the previous...remove the old and install new...or just add more fiberglass over the top and be done with it. Adding fiberglass over the cellulose solves the shrink issues completely.


I went into my attic with an electric weed Whacker/weed trimmer and I pulverized the old compacted sheets of loose fill to where the consistency was even fluffier than with a blower machine. Obviously I had to be careful on the rafters and not whack electrical cords too much. The plastic trimmer line I use is pretty soft, so it didn't damage any romex at all even though I accidentally whacked it a few times. Definitely wear goggles and N95 and full body clothing to keep the stuff off and out of your body. I also used the trimmer to expand and pulverize 3 new bales of loose fill insulation and it again fluffed it to a greater volume than when I used a blower years ago.

  • 1
    Even a minor weed whacking of the housing of NM-B cabling ("Romex") isn't a good thing.
    – FreeMan
    Commented May 30, 2022 at 11:07

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.