Wall insulation (cellulose v/s fibreglass)

Hi, Cellulose tends to absorb moisture and sag compared to fiberglass. Known fact from the field experience. Have enough on the ceiling? Good luck, Tony

cellulose settles and also causes dust in your house 24/7 when not entirely sealed from the interior of your house (tough to do, hvac ducting breathes and cellulose gets in); cellulose is usually recycled newspaper with fire retardent added; cellulose can be about a 30% radiant barrier; cellulose seals against (stops) wind - wind doesn't go through it; if cellulose gets wet it is destroyed

fiberglass is glass fibers; fiberglass is not a radiant barrier; fiberglass doesn't seal against (stop) wind - wind goes through it; if fiberglass gets wet it can be dried and reused

My home circa 1999 has fiberglass for all of the vertical and cellulose for all of the horizontal.

I'm guessing..... ah you see those shows with the houses invaded with black mold, well on those shows the bad mold loved wood and paper products. So, speculating that if the celluous gets wet you have a potentially serious health problem.

On the plus side of cellulose, it has a higher r value per inch.

later,

tom @

and in extreme temps, fiberglass loses some of it's insulative properties... or so I've heard.

Dense pack cellulose shouldn't settle much. (top it off in 5-10 years perhaps?)

Wet pack cellulose doesn't settle at all. (held in place by a glue matrix i think)

I also think cellulose has a higher r value.

fiberglass = no need to top it off in 5-10 years

it can

unless more fiberglass is used ; )

If your insulation is getting wet enough to cause a major mold problem, you have major problem that don't relate at all to insulation. Cellulose can get damp or wet and dry out. If it gets wet repeatedly, it will lose its boric acid, which acts as fireproofing.

Fiberglass has so fireproofing properties.

well... with less R in the walls.

don't have it in front of me, but i thought the OP was retrofiting wall cavities. kinda hard to put a 2 inch thick layer in a 3.5 inch thick cavity.... ;)

I've been pondering the best route to go insulation wise for a while now. I'd really like to go foam... best R per inch and seals air leaks. Cellulose is a close second. (next best R and some air infiltration protection)

I can't seem to find anyone who'll do the foam locally. there is a DIY site with a low expanding DIY foam...

Depends on how it is put in. Fiberglass in batts doesn't sag. Fiberglass blown in does. Flat on the ceiling, 15 inches of blown in fiber glass will compress to about 1/2inch when stepped on and will stay that way. a 6 inch batt will rise back to 5-1/2 inches almost immediately. Don't know how you would put stuff in your walls without blowing it in. The blown in dry fiberglass will settle, so will blown in dry cellulose.

You don't say what you are insulating against, heat/cold or sound.

Most thermal insulators perform poorly as sound blockers. Some actually enhance sound transfer. (Like well packed insulation and expandable or "pour-in" foam).

Fiberglass and cellulose have some minor sound reduction qualities some would say- in practice, it doesn't.

For both sound and thermal insulation, cut wool fibers are best.

If sound is the issue, more info at

BJ Nash

Tip: Using a E-mail program that is not susceptable to control by hackers makes sense to me... I use Agent: It's free and available from

BJ Nash Super Soundproofing Senior Technical Advisor Super Soundproofing Co.