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Thread: Cotton Batting

  1. #1
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    Cotton Batting

    I have read about and personally used cotton batting (aka cotton insulation, aka upholstery foam batting) to stuff and fill the crevices in a car. So far I have only done my hatch and rear panel trim. Personally, this went over a layer of butyl based sound deadener and mass loaded vinyl. I was surprised to notice a huge change in the overall background noise, particularly at highway speeds, after only doing half the car (sadly no objective evidence to substantiate this claim). I want to get a discussion going about individuals' experience with cotton batting and any insights as to whether it is viable independently and/or as an adjunct for other more traditional methods of deadening.

    It obviously has value in reducing panels from vibrating against one another. Given its low cost it would be interesting to learn if there is any evidence for it doing anything more in the amount/thickness that is realistically usable in a car.
    Last edited by trevordj; 09-28-2010 at 12:28 AM.
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    Tester Extraordinaire ErinH's Avatar
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    I did the same a couple years back. I stuff voids in the pillar (b, c) and crevices wherever I could. I also used various types foam/fill to stuff the dash with and even the center console area. It also made an impact on overall road noise attenuation.
    At the time, I had taken a strip of sound deadener and applied it to the outer portion of the bpillar. Then on the opposite pillar, I stuffed the cavities with polyfill. I did the 'knock' test and the cavity filled pillar was much more 'dead' than the other one. Not very scientific, but you get the idea. Stuffing the voids helped to reduce of flex/vibrations in the areas where fill was stuffed in to.

    As cheap as it is to do ($10/5lb bag of polyfill), it can't hurt to try.


    A bit OT, but FWIW I've also been turned on to using wool instead of polyfill in my kicks. I noticed that my resonance issues diminished much more with the wool in place than with the polyfill in place, although the woofer tester didn't show any significant improvement.
    Last edited by ErinH; 09-28-2010 at 07:51 AM.
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    gyroscopes and infrared FoxForce's Avatar
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    I sold recycled cotton and have quite a bit in my car.

    What's really pertinent of a discussion is how absorption works. Sounds enters the "cellular matrix" of the absorber and gets lost/traped and is converted to heat. In order for this to happen, the material has to have air and space to do so. So often I hear of people stuffing foam or cotton into spaces; bad idea. Take a sponge and squish it into your hand (remove the air, increase the density) and stick it under water. The more you release your fist the more water it absorbs. Ie, density and absorption are inversely related.

    That said, I think an open cell absorber material is not wise choice for a mechanical isolator for decoupling vibrating surfaces. You don't see gaskets made of open cell foam. Something closed cell or resilient rubber would be better (think of the material of door seal in a car door.)

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    Quote Originally Posted by FoxForce View Post
    I sold recycled cotton and have quite a bit in my car.

    What's really pertinent of a discussion is how absorption works. Sounds enters the "cellular matrix" of the absorber and gets lost/traped and is converted to heat. In order for this to happen, the material has to have air and space to do so. So often I hear of people stuffing foam or cotton into spaces; bad idea. Take a sponge and squish it into your hand (remove the air, increase the density) and stick it under water. The more you release your fist the more water it absorbs. Ie, density and absorption are inversely related.

    That said, I think an open cell absorber material is not wise choice for a mechanical isolator for decoupling vibrating surfaces. You don't see gaskets made of open cell foam. Something closed cell or resilient rubber would be better (think of the material of door seal in a car door.)
    How loose should it be placed in order for it to be the most effective? Packed but not jammed in there? Lightly packed? How it came in the package? Fluffed up?

    I guess a jig could be built that would allow someone to measure how different densities absorb sound. Something like a shallow wide and tall 7" enclosure. With the driver inverted on one side (internally protected by a screen) and on the other side no back panel, just a removable rigid screen that you can take off and pack in different amounts and materials to see what combination works best. Then the mic on the other end.

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    Quote Originally Posted by FoxForce View Post
    I sold recycled cotton and have quite a bit in my car.

    What's really pertinent of a discussion is how absorption works. Sounds enters the "cellular matrix" of the absorber and gets lost/traped and is converted to heat. In order for this to happen, the material has to have air and space to do so. So often I hear of people stuffing foam or cotton into spaces; bad idea. Take a sponge and squish it into your hand (remove the air, increase the density) and stick it under water. The more you release your fist the more water it absorbs. Ie, density and absorption are inversely related.

    That said, I think an open cell absorber material is not wise choice for a mechanical isolator for decoupling vibrating surfaces. You don't see gaskets made of open cell foam. Something closed cell or resilient rubber would be better (think of the material of door seal in a car door.)
    Why is that? The way I have used it and the way I think about it is it tightens the gap between two panels that are otherwise free to resonate against one another. I have had success using it this way, but is there a reason something like closed cell foam is better at this job (I have used this as well and haven't noticed a difference one way or the other)? I haven't seen gaskets made of open cell foam but generally think of a gasket as sealing something rather than primarily functioning as a decoupler.
    -Trevor

  6. #6
    Tester Extraordinaire ErinH's Avatar
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    ^ agreed.

    I've done it. It works well. Is cheap as heck to boot.
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    gyroscopes and infrared FoxForce's Avatar
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    Quote Originally Posted by trevordj View Post
    Why is that? The way I have used it and the way I think about it is it tightens the gap between two panels that are otherwise free to resonate against one another. I have had success using it this way, but is there a reason something like closed cell foam is better at this job (I have used this as well and haven't noticed a difference one way or the other)? I haven't seen gaskets made of open cell foam but generally think of a gasket as sealing something rather than primarily functioning as a decoupler.
    Sure, as long as that gap doesn't want to be closer to each other. If whatever you're trying to keep apart wins and your ____ gets compressed over time, then what good is it?

    Not saying it's wrong or bad, just saying with all the stuff out there....there's probably something more applicable. Kind of like layering 18 sheets of VE damper to make a barrier. We know, as we have beaten this to death, it's not very intelligent....but if you really really want to make it, then it can.

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    Quote Originally Posted by FoxForce View Post
    Sure, as long as that gap doesn't want to be closer to each other. If whatever you're trying to keep apart wins and your ____ gets compressed over time, then what good is it?

    Not saying it's wrong or bad, just saying with all the stuff out there....there's probably something more applicable. Kind of like layering 18 sheets of VE damper to make a barrier. We know, as we have beaten this to death, it's not very intelligent....but if you really really want to make it, then it can.
    That's exactly what I wanted to get at. Is this just another peel and seal fiasco or does it have legitimate utility in a car? It seems you are thinking not, which is fine, but it seems to be based on the presupposition that this stuff compresses over time as an open cell foam does. Is this the case? I don't know; I have only had it in my car for about 1 month. It certainly doesn't have the feel of open cell foam however; it feels more like a really thick t-shirt. There is no evidence of compression in that amount of time as far as I can tell. Maybe Erin can give us some insight if the batting he placed has compressed since he has had it in longer and has recently (re) torn his car apart.
    -Trevor

  9. #9
    Tester Extraordinaire ErinH's Avatar
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    the stuff I used was polyfill. I stuffed it in crevices, so yes, it was compressed.
    Mine's in the b-pillars, trunk deck, trunk lid and crevices in the trunk. The dash is stuffed with polyfill/wool/eggcrate foam, and the console is stuffed with polyfill and eggcrate foam.

    Again, for as cheap as it is, it can't hurt to try. If it doesn't work, turn on the vacuum and get it out of there. No need to take guesses on something this simple. Just give it a try.
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  10. #10
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    now, i'm now quilter, but unless there is constant pressure being applied to my quilts, they don't compress. so, over time i can see how batting can "settle" if you will, but not shrink to useless levels.

    i'm intrigued by this thread and would like to see some testing. what type of batting are your guys using? any special brand or type?

    edit: erin you posted just before i did, basically answers all my questions

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