Roxul vs Fiberglass Insulation for Soundproofing

When I was working on making my quiet office, I looked for information on Roxul vs. fiberglass for soundproofing the walls and ceiling. Everybody seemed to have an opinion. As I finished my office, friends, and family, and even clients started asking what I’d used and why.

I could have given them a list of all the sites I checked out. There are a lot of articles out there full of numbers, information, graphs, and pictures. I decided to put what I found together for them, and share it with you too.

Soundproofing and Sound Absorption

There are four parts to soundproofing – decoupling, mass, damping, and absorption. Decoupling is about separating walls and ceiling into layers to decrease sound transfer.

Adding mass makes it more difficult for sound waves to pass through. Damping prevents sound from vibrating from one layer to another to travel into another room or floor.

Insulation is about absorbing sound waves. Whether you’re trying to prevent sound from being transmitted into other rooms or trying to improve the sound quality within a room, insulation works.

Soundwave vibrations penetrate the insulation. Some of the vibrations are absorbed and converted to kinetic energy or heat, reducing the number of sound waves passing through or returning. The argument here is what insulation works better, Roxul, or fiberglass.

 

What Is Roxul Acoustic Insulation

Roxul acoustic insulation is stone wool insulation that absorbs sound waves, is fire resistant, and is manufactured by a company called Roxul. It is dense, yet porous, and reduces the movement of heat or cold, plus it absorbs sound waves and vibrations.

What is Roxul made of?

Roxul is made of mineral or stone wool which spun from molten slag or igneous rock. A cubic foot of rock makes 37 cubic feet of stone wool. It has a melting point of 2150°F so isn’t combustible, and it doesn’t absorb moisture.

Uses of Roxul insulation

Roxul is used in the walls, ceilings, and attics of homes and in planes and vehicles to reduce the movement of heat, cold, or sound. It is used in engine compartments to control heat and sound transfer, around hot or cold pipes to decrease temperature loss, and in machinery rooms and housing to decrease sound and heat movement. It is also used in some hydroponic applications.

Is Roxul good for soundproofing?

The dense porous stone wool that Roxul is made of makes it a good insulator for heat and cold, and also for sound. The thicker or more dense the batten or panel, the more sound it will absorb at different frequencies.

Roxul products have a density of 2.5 lb/ft³ to 8.0 lb/ft³.  Different densities work better with low range frequencies, others at mid or high frequencies. The NRC (noise reduction coefficient) measurement of Roxul is 0.95 or better.

Does Roxul Safe’n’Sound have an R-value?

Safe’n’Sound is intended for interior walls, floors, and ceilings. Since it isn’t intended for exterior wall use, it isn’t given an R-value. However, it has been tested by Roxul, and the 3-inch batt has a value of R11.7.

How long will Rockwool last?

Rockwool doesn’t slump or suck up moisture like a sponge, nor will it shrink of crumble. It will last as long as the building. Presently, it is only given a lifespan of 100 years.

Is Rockwool dangerous?

Like all fiber or wool material, rockwool can irritate the skin and eyes when working with it. It is recommended that gloves, a dust mask, and eye protection be used. The fibers are monofilament strands, and unlike asbestos, the body can expel them easily if breathed in. It isn’t carcinogenic according to the IARC (International Agency for Research on Cancer).

 

Roxul Acoustic Insulation Sound Properties

The acoustic properties of different Roxul products depend on their thickness and density. Safe’n’Sound has a density of 2.5 lb/ft³, an STC (sound transmission class) of 45 on 16” center wood studs, 52 with 24” center steel studs, and 50 when used between floor joists.

The NRC (noise reduction coefficient) is 1.05 for a 3” thickness too.

A 2” thickness of Rockboard 60 has an NRC of 0.95, and Rockboard 80 is 1.00, and acoustic fire batts (AFB) bounce in at 0.95. The 3” thick Safe’n’Sound ranks better overall for sound control, especially at the lower frequencies.

 

What Is Fiberglass Sound Insulation

Fiberglass sound insulation is made of plastic wool embedded with tiny glass shards. It is fire resistant unless paper backed. It is manufactured by Owens-Corning (OC) and other companies.

The insulating properties that trap air and reduce the movement of heat and cold, also make it good for controlling sound waves and vibrations.

What is fiberglass made of?

Fiberglass is made of silica (sand) that has been melted and spun into glass wool. The wool is reinforced with tiny fibers of glass. Fiberglass will not burn, but it may melt if temperatures go above 212°F.

Uses of fiberglass insulation

Fiberglass insulation is used in walls, floors, and ceilings to control the movement of heat, cold, and sound. It’s used in vehicles and planes for the same reasons too. It is used to wrap pipes, blanket machinery, and to decrease the effects of noise, heat, and cold. It’s even used in the space shuttles!

Is fiberglass good for soundproofing?

The properties that make fiberglass good for controlling heat and cold also make it good for sound control. Like other insulation materials, the thicker and denser the material, coupled with internal airspaces, the better it absorbs sound.

Owens-Corning has products that range from 1.5 lb/ft³ to 8 lb/ft³. Some perform better with mid to high range sound frequencies, others at the low end. The Noise Reduction Coefficients (NRC) for O-C products range from 0.50 to 1.15.

Do fiberglass sound attenuation batts have an R-value?

Sound attenuation batts come in fire rated and non-fire-rated, with Kraft paper backing or foil backing or with no backing. This insulation is intended for interior walls and not given an R-value; however, the 4-inch thick sound attenuation batts have an R11 rating.

How long will fiberglass last?

Fiberglass should last for upwards of 80 years if it is inside a wall, floor or ceiling cavity, and isn’t exposed to moisture or rodents. However, the main problem with fiberglass battens and rolls will slump and compress over time.

This can lead to uninsulated pockets and a reduction in R-values. The rigid panel products don’t have this problem but are more expensive.

Is fiberglass dangerous?

Fiberglass can irritate the skin, eyes, nose, and throat and make breathing difficult. When handling it, the skin should be covered, and gloves, eye protection, and a dust mask should be worn.

Fiberglass particles can become airborne if left exposed as in an unfinished basement. It is recommended it be covered with plastic or another impermeable material.

The small glass particles floating around and being inhaled is a concern. Testing has shown that it is a respirator carcinogen in animals similar to asbestos, but definitive research has not been done, so it isn’t classed as a carcinogen in humans.

 

Fiberglass Insulation Acoustic Properties

The acoustic properties of fiberglass are based on its thermal characteristics. Whether the insulation is batten, panels, board or mat, the density, and thickness impact the sound absorption ability.

Most acoustic fiberglass has a density of 1.5 lb/ft³, 3 lb/ft³ or 6 lb/ft³ and an NRC rating between 0.65 at 1” thickness and 1.15 and 4” thickness.

Using O-C QuietZone 4” thick acoustic insulation in wood stud interior walls at 16” or 24” centers, the STC value is 34, and 38 with steel studs. Using 4” of O-C 703 series gives an NRC of 1.15, with better than average (NRC 0.75) results at the lower frequency range.

Bumping the thickness up to 6-inches provides even better results.

 

Roxul vs Fiberglass Insulation for Soundproofing

Comparing Roxul or Rockwool with fiberglass insulation for soundproofing isn’t quite like comparing apples to oranges. However, if we focus on two similar and popular sound control products from each insulation type, a comparison works better.

Remember, insulation addresses only the absorption part of soundproofing – decoupling, mass, and damping are the other parts.

The characteristics that make insulation good at keeping heat and cold in or out of a space are also the characteristics that make it good for soundproofing. Soundwaves enter the insulation, and some sound vibrations are trapped in air pockets, and converted to kinetic or heat energy. This conversion decreases the sound bouncing back into a room, or passing on to another room.

If you’re looking at improving sound quality in an existing room, and don’t want to take walls or ceilings apart to install insulation, check out 21 DIY Acoustic Panels Ideas and Plans. It has some great suggestions to help you out.

InsulationThicknessR-ValueDensityNRCSTC in 2×4 Wall with ½” drywall on both facesCost per Square foot (USD)
Roxul Safe’n’Sound 3”

R-112.5 lb/ft³1.0545$0.73
O-C Sound Attenuation Batts3½”R-91.5 lb/ft³0.9043$0.67
Rockboard 60 panel 2”

R-96.0 lb/ft³0.9546$1.14
O-C 703 panel 2”R-8.73.0 lb/ft³0.9045$1.40

Installation

Both Rockwool and fiberglass batts are cut to fit between studs at 16” and 24” centers. Rockwool is dense and rigid and holds its form when placed between studs; it friction fits between the studs. Fiberglass batts aren’t rigid and tend to slump inside wall cavities and must be paper backed.

Fire Resistance

Stone wool has a higher melting point than glass wool and is more resistant to fire, moisture, mildew and mold, insects, and rodents.

Best Uses for Both

The four products in the table above are commonly used to absorb sound in buildings. It can be used in wall and ceiling cavities, or as the absorbing mass in acoustic panels, bass traps, and other sound improving devices.

Roxul and fiberglass have similar acoustic properties when compared to similar products. The stone wool insulation is slightly more expensive, but I did find Safe’n’Sound on sale for less than fiberglass.

It’s also interesting to note that Owen-Corning is moving into mineral wool insulation manufacture too.

Rockwool is easier to work with than fiberglass and is better for acoustic panels than fiberglass. It is also better at absorbing low-frequency range noise than comparable fiberglass.

I recommend using Roxul in acoustic panels and traps, and use the fiberglass in wall and ceiling cavities where it is fully closed in. In damp locations, rock wool retains its thermal and acoustic properties whereas fiberglass deteriorates, so use the material that works best for the purpose you need it for.

Note: Ensure the insulation is covered to prevent particles from escaping and causing health risks.

Conclusion

You can use insulation to improve the sound quality within a room or to decrease the sound filtering into other rooms. Whether you chose Roxul or fiberglass may be a matter of cost, availability, and even personal preference.

My preference is Roxul or Rockwool as it is now being called. It’s easier to handle, less expensive where I live, fewer health risks, and works better for the same thickness of insulation.

Your feedback is appreciated. If you know someone interested in soundproofing, pass the article on to them.

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