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I have an old car (FIAT Panda, 1993) which has basically no sound insulation. I like to work on the car to improve it, so I thought about sound insulation. I'm not looking to improve sound deadening of the interiors.

At this time I have almost all the info I need, but I would like to know which material is best suited to proper insulation.

Doors: they cannot be "opened" in two, the two sides are welded together, so I will put bitumen bands on the inside, the strips meant for roofs like http://www.bostik.nl/nl_NL/toepassingen-en-producten/zoek-op-segment/bouw/BatuBand/SCNL0206/producten-3/?detail=1 because Dynamat and similar are too expensive.

Hood and engine compartment: if there are exposed parts of chassis that resonate, bitumen strips, plus (according to ease of application and securing) rock wool.

Trunk: on the bottom below the floor covering, bitumen strips if needed and either rock wool or foamed laminate underlayment (http://www.bestlaminate.com/vapor-3-in-1-blue-underlayment-100-sq.ft-roll/). This underlayment is rated to >10 dB attenuation (I suppose for impact noise).

Inside the vehicle, floor: for sure laminate strips where the chassis resonates, plus either rock wool or foamed laminate underlayment below the soft plastic flooring.

My doubts are all about foamed underlayment vs rock wool.

What are the pros and cons of each alternative? keeping also in mind that I cannot easily find rock wool thinner than 30-60 mm (not under compression).

In the engine compartment rock wool is the only option due to temperature and environment, but below the internal flooring I'm unsure what to choose.

  • Personally I'd avoid rock wool except when necessary. It's harder to cut and shape, and annoyingly itchy. Depending on the composition, there could also be health concerns with inhaling the fibers. – barbecue Sep 19 '15 at 23:07
  • I would also point out that the underlayment you linked to is very thin, and intended to serve as a vapor barrier, it's not going to provide much sound insulation. I think you'd do better to look for acoustic foam, or even spray foam. – barbecue Sep 19 '15 at 23:11
  • @barbecue The underlayment is rated for 10 dB sound insulation, at least for impact noise. I have acoustic foam (the piramidal one?) but I don't have much space between floor and chassis, and the foam when is compressed becomes less effective. laminaat.nl/isogold.html – FarO Sep 20 '15 at 13:35
  • @ OlafM, The link in your original question was to a vapor barrier product. The isogold product is the same kind of product I mentioned in my answer. – barbecue Sep 20 '15 at 14:54
  • Good point. I will check what is available in the local hardware store keeping in mind that some are meant for vapor and get noise as side effect, and for others sound is the priority. – FarO Sep 21 '15 at 8:42
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My recommendation would be to go with a foam-based product that's specifically designed for acoustic dampening.

Noise dampening insulation basically comes down to two things: absorbing or blocking the sound, and reducing/eliminating the movement of parts which leads to vibration and rattling noises.

Foam products can help with both functions. There are a variety of brands available specifically designed for use in cars, such as Cascade Audio, Second Skin Audio, and RAAMaudio.

The down side is many of these products are fairly expensive, as they tend to cater to car audio aficionados. However you may be able to research the kinds of products they provide, and then find similar but less expensive materials from a company that sells generic foam padding or insulation, such as Isogold foam.

Mineral wool products are commonly used in soundproofing homes, because of their low cost and ease of installation as flat sheets behind walls, but in a car, you are going to have to deal with unusual shapes and curved surfaces, and cutting and forming mineral wool to conform to the required shapes will be more difficult. You'll also risk skin and eye irritation, so if you do use them, be sure you wear gloves, eye protection, and a long-sleeved shirt. Also, if you do get get mineral wool dust on your skin, don't scrub it off, as that will increase the irritation. Rinse it with running water instead.

A difference between home and car sound insulation is that more of the noise in a car comes from vibration and rattling, and foam products will be more effective at damping those vibrations than mineral wool products.

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  • If you can get a source or reference for the sentence (foam vs wool), the answer will be much better and perfectly complete :) – FarO Sep 21 '15 at 8:44

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