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What's the difference between mineral wool and fiberglass bat insulation ?  

post #1 of 11
Thread Starter 
Is there any advantage to using mineral wool compared to regular fiberglass bat insulation ? I will be using 2 layers of drywall with Green glue on walls and RSIC-1 and 2 or 3 layers drywall and GG on ceiling. Is there any benefit to using mineral wool versus fiberglass insulation ?
post #2 of 11
I would tend to think that if you have 2 layers of drywall the mineral wool is ok to use, but it might be a little over kill (inside the walls). Not to say it would not help, but it is not used for soundproofing. Save it for inside the room, would be my advice.

post #3 of 11
Thread Starter 
Where would you use it inside the room ?
post #4 of 11
that is a bigger question then you think! :) They can be used for bass traps in corners and also for reflection points throughout the room.
Do a search on here for acoustic panels and you will see what I am talking about. There are also pictures on our website you can check out.
post #5 of 11
Once again the great work of BasementBob can be referenced

post #6 of 11
basement bobs absorption page is not a bit shy of brilliant. it rules.

for sound isolation, the impact of insulation can be broken into three basic categories

1. absorbing noise going through the air cavity
2. lowering the frequency ofmass-spring resonance (important for decoupled walls like your ceiling, not as important for purely damped or simple conventional 2x4 walls)
3. damping the mass-spring resonance (it's value here is higher for decoupled walls, wher ethe air in the cavity plays a role, than for direct-screwed walls, where the resonance is mostly mechanical)

1. affects mid/high frequency TL
2. affects low frequency TL
3. affects low frequency TL

hence we could probably say that 2 and 3 are more important than 1, as if your wall has problems stopping mid/high frequencies, it probably has seal problems, or is simply a horrible wall. your wall won't have such problems if properly sealed unless ductwork or something proves your undoing.

how they rank (i base this on existing data)

1. mineral fiber is plainly superior

2: fiberglass is best. if too dense of a fiber (like, for example, rigid fiberglass) is used, this area of performance gets WORSE (i can reference specific NRC tests if you like)

3: mineral fiber is a bit better (we did a big study on this in our labs once), BUT, none of the fiber products will really supply alot of damping, and the difference is not that significantin the grand scheme of things

whenever someone asks, i recommend just using fluffy fiberglass. And i mean that.

post #7 of 11
Hello Brian

You made the comment that if dense FG is used it gets worse. What fiberglass is to dense? I don't want to use the wrong stuff.

post #8 of 11
plain old off the shelf fiberglass works as well as anything.

When i say "too dense", i don't mean common mineral fiber, actually, hold that thought, i'll spend a minute and dig through known data to get a more accurate thought for you.

but plain old john mansville or owens corning or (other brands) is as good as anything.
post #9 of 11
Thanks for the clarification. I just bought my insulation this weekend and thought I might be in trouble.
post #10 of 11
although it can be a pain in the rear, and digging through documents like this might be confusing at first, you can often find the answers to nearly any question about sound isolation (or at least many questions) at www.nrc.ca. that's the site of the National Research Council of Canada, and they have probably the largest collection of publicly available data on earth, and almost certainly the largest collection of data including low frequency information (lower than the STC range).

for 2.5" steel studs, using

-boring old fiberglass (0.7 pounds/cubic foot), STC=39, OITC=25, M&T=26.4
-normal mineral fiber (2-2.2 pcf), STC=38, OITC=25, M&T=26.2
-higher density mineral fiber (2.75-3pcf), STC=36, OITC=24, M&T=25.4
-extremely high density mineral fiber (6pcf), STC=37, OITC=25, M&T=26.3

so none outperformed plain old boring off-the-shelf fiberglass for all-around performance, although all had clearly superior mid/high absorption characteristics.

in other comparisons from the NRC's document IR-761, the same basic trend is observed: the low frequency resonance shifts up as density goes too high, and that negates whatever advantage mid/high frequency gains yield, and the glass tends to perform at least as well as anything.

hence i recommend just using fiberglass. That said, mineral fiber of normal density doesn't prove itself WORSE than fiberglass, so use that if you like, but avoid extremely high density materials like specialty fibers that are very dense... use those for room treatments!

post #11 of 11
hey, folks, please note that i had a type-O in the post above

one line said STC=73, when it should have been 37, is fixed now, apologies for any confusion
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