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Rockwool vs Fiberglass Sound Insulation

Rockwool vs Fiberglass Sound Insulation

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The National Institute of Building Sciences reports that acoustics is one of the most commonly overlooked factors in obtaining a comfortable environment is essential for obtaining optimum performance from employees.

Builders and homeowners can apply acoustic insulation to services to prevent them from transmitting noise. This feature is becoming increasingly important in construction, whether it’s for renovation or new projects. In addition to the benefits of acoustic insulation for worker productivity, construction projects are more likely to require it to comply with building codes.

Selecting between Roockwool vs fiberglass as the best choice for a particular project requires you to compare many characteristics between them.

Acoustic Insulation & Sound Absorption

Acoustic insulation is a key component of soundproofing an interior space and is typically an integral component of surfaces such as ceilings, floors, and walls. Managing the acoustic of a built environment generally involves either absorbing sound waves or blocking them entirely. A wall containing acoustic insulation is one of the most common examples of such a sound barrier.

Most buildings combine both types of insulation to reduce the transmission of sound. Absorbing sound waves dampen or deaden, the sound. Soft materials such as carpets, fabric panels, and perforated ceiling tiles are typically used for this purpose. Blocking, or isolating sound requires the builder to consider the design of the space as well as the material itself.

Rockwool Acoustic Insulation

Manufacturers make stone, or mineral, wool by heating rock to a temperature of about 1,600 degree Celsius while blowing a stream of air over it. Advanced techniques also spin the molten rock at high speed in a process somewhat similar to that used to make cotton candy. This process converts the rock into a mass of intertwined fibers with a diameter between two and six micrometers (μm). Mineral wool may also contain binding agents and oil to reduce dusting.

Mineral wool has a high resistance to heat, making it a popular choice for passive fire protection. Builders typically use it in spray form to fill stud cavities in drywall and to make fire stops. Mineral wool also conducts heat well when pressed into rolls and sheets. In addition, their ability to partition air in these forms makes them excellent sound absorbers.

Rockwool is a company that makes its own brand of mineral wool, which is composed of basalt rock and recycled slag. Basalt is a type of rock produced by volcanic activity, so it’s abundant in the earth. Slag is a by-product of metal refinement, primarily steel and copper.

Fiberglass Acoustic Insulation

Fiberglass is a type of plastic that’s reinforced with glass fiber. The plastic matrix is typically a thermoset polymer such as epoxy, polyester resin, or vinyl ester. The fibers may be used in various ways, including flattening them into a sheet, weaving them into a fabric, or simply arranging them into random patterns.

Owens Corning makes many types of fiberglass, including Types 703 and 704. The most common uses for these types are thermal and acoustic insulation due to the ability of these fibers to absorb energy. Type 703 is a semi-rigid board used in ceilings, walls and ductwork, and mechanical equipment. Type 705 is a rigid board used for the same general applications as Type 703. However, 705 has greater strength, so it’s more appropriate for harsher environments.

Both types of fiberglass have a choice of facings, including Foil/Reinforcement/Kraft (FRK) and All-Service Jacket (ASJ). FRK is a vapor retardant laminate made of foil reinforced with scrim and kraft, while ASJ is made of bleached white foil reinforced with kraft.

Rockwool vs. Fiberglass for Soundproofing

Selecting the best material for insulation and soundproofing often comes down to a choice between Rockwool and fiberglass. This process involves a comparison of these two materials in the following areas:

  • Sizes
  • Density
  • Noise reduction
  • Insulation
  • Heat resistance
  • Cost
  • Safety
  • Environmental concerns


The most common sizes for Rockwool are sheets measuring 24” x 48” and 16” x 48”. Larger sizes are also available, although they typically require a minimum order quantity. The board products can be up to 6” thick and the batt products can be up to 7.25” thick, depending on the application.

Type 703 and 705 Owens Corning fiberglass is readily available in lengths ranging from 24” to 121” and widths from 45” to 49”. Typical thicknesses for these types of fiberglass range from ¾” to 4” for 703, and ½” to 2 ½” for 705. The size may also affect the minimum order requirements and lead times. Contact your local area sales manager for details.


Density is a measure of mass per unit volume and is usually expressed in terms of pounds per cubic foot (lb/ft³) or kilograms per cubic meter (kg/m³). It’s also important to note the standard used to determine the density of insulating material. Density is an important consideration for some applications where the insulation has significant weight.

The density of Rockwool is 2.4 lb/ft³, or 38 kg/m³, and is based on the ASTM C167 testing standard for density. Owens Corning Type 703 has a density of 3.0 lb/ft³, or 48 kg/m³. Type 705 has a density of 6.0 lb/ft³, or 96 kg/m³. Both types use ASTM C303 as their testing standard.

Noise Reduction

The Noise Reduction Coefficient (NRC) describes a material’s average sound absorption across a range of frequencies. An NRC of 0 indicates the material doesn’t absorb mid-frequency sounds at all, while an NRC of 1 means the material has an acoustic surface area equivalent to its physical surface area. Materials can have an NRC value greater than 1.

Rockwool Safe’n’Sound is the most common form of this material for insulation. It’s ideal for interior wall applications requiring sound absorbency and heat resistance. 1 Safe’n’Sound batt with a thickness of 3” has an NRC of 1.05, while a thickness of 6” has an NRC of 1.15. The sound absorbency of Rockwool insulation is based on ASTM C423.

The noise reduction of fiberglass insulation depends on its type and thickness. The following table shows this relationship:

ProductThickness (in)NRC
703 Unfaced 1.00.70
705 Unfaced1.00.75
703 FRK1.00.65
705 FRK1.00.55
703 ASJ1.00.65
705 ASJ1.00.50


Insulation is expressed as an R-value in the context of building and construction. This value measures how well a two-dimensional barrier like a layer of insulation resists the flow of heat through it. More formally, R-value is the difference in temperature per unit of heat flux need to sustain the flow of one unit of heat flux between the two surfaces of a barrier under constant conditions. A higher R-value indicates greater insulation.

Rockwool has better insulation than fiberglass. The R-value of Rockwool is about 3.0 to 3.3 per inch, depending on the type. The R-value of fiberglass is between 2.2 and 2.7 per inch, depending on type and configuration.

Fire Safety

Rockwool is a better choice for fire safety because it has a higher melting point than fiberglass. The melting point of Rockwool is up to 1,800 degrees Fahrenheit or 1,000 Celsius. Rockwool is non-combustible and has smoldered resistance of 0.09 percent at 750 degrees Celsius, making it effective for containing a fire. It’s Type 1 compliant for blanket thermal insulation for buildings.

Type 703 and 705 fiberglass melts at about 600 degrees or 1,100 Fahrenheit. The faced versions of both types of material have a flame spread index of 25 and a smoke-developed index of 50. The unfaced versions have a flame spread index of 5 and a smoke-developed index of 5. The standards used to determine these surface burning characteristics include ASTM E84, CAN/ULC-S102, and UL 723.


Rockwool costs about $1.30 per square foot, depending on the thickness and density. For example, a package of six sheets measuring 4’ x 2’ with a thickness of 2” and standard density costs about $55. Doubling the thickness to 4” increases the cost to about $66. A package of six sheets of high-density Rockwool board with these dimensions and a thickness of 2” costs about $75.

The cost of fiberglass is highly dependent on type. A package of Owens Corning 703 acoustic board with FRK facing costs about $85, assuming a total area of 48 square feet and a thickness of two inches. The same package costs $125 for 705 acoustic boards.


The biggest health risk for insulating materials like Rockwool and fiberglass is from inhaling the fibers. Traditional Rockwool is quite harsh on the lungs, but HT Rockwool is one of the safest insulators available. Its fibers dissolve easily in the lungs and appear to be completely non-carcinogenic.

The fiberglass used for insulation also seems to be quite safe. It has no history of causing lung cancer, even during long-term exposure. However, type 703 fiberglass has fibers that are much more abrasive than those of HT Rockwool, so it’s at least theoretically capable of causing greater lung irritation. This is particularly likely in cases involving a high level of unprotected exposure.

Regardless of the specific material, you should always wear protective equipment when installing sound insulation, including masks and gloves. Manufacturers are also trending towards production techniques that further reduce the health risk of their products. These features include tighter weaves and batting around the insulation to prevent fibers from separating from the insulation.

Environmental Concerns

Rockwool and fiberglass are both ecologically friendly compared to other building materials. About 75 percent of the material in Rockwool can be recycled, while only 20 to 30 percent of the material in fiberglass is recyclable. However, Rockwool still contains formaldehyde binders, which fiberglass insulation hasn’t had for years.

Final Thoughts

Managing interior noise is becoming more important to both builders and homeowners, but it doesn’t need to be a complicated process. It begins with selecting the material to use, which often comes down to a choice between Rockwool and fiberglass. Rockwool is more expensive, but it generally has more favorable qualities than fiberglass for both thermal and acoustic insulation.

Tom Davidson

I'm a Design Engineer, husband, and Dad to two. I have a taste for building, playing bad golf, and tackling all kinds of home improvement projects. Read more about the SPT Team.

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