Are you planning to build a house and wondering what insulation material is best to use? 

House insulation is a rigorous job. It is especially more difficult now that there are several different insulation products available in the market, making it hard to choose which one to use.

Fiberglass and mineral wool are two of the most used materials to insulate residential and commercial buildings today. Both products provide excellent performance in terms of heat, fire, and even sound resistance. Still, these two are two separate materials and have differences.

As such, in this blog post, we will discuss both mineral wool and fiberglass insulation and compare each of their characteristics.

Fiberglass Insulation: What You Should Know

Fiberglass is the most accessible, affordable, and easy-to-install insulation material to slow the spread of heat, cold, and sound in buildings. These qualities made fiberglass the most popular insulation material among homeowners across the US.  

Fiberglass is generally made of fine-grained glass substances. It has a natural brown or white color but is often seen with a bubblegum pink color due to the pink polymer glue sprayed during the manufacturing process. 

The fiberglass manufacturing process involves combining several different raw materials with recycled glass. These include silica sand, limestone, soda ash, magnesite, and borax. Other manufacturers do use kaolin clay, nepheline syenite, calcined alumina, and feldspar as well.

The combined material is then heated at a high temperature until molten which is then placed inside a perforated metal container that has thousands of tiny slits. The strands of substance that come out of the container then fall into a conveyor belt which is layered and interlaced together to form a wool-mat-like material.

Most manufacturers used 40% to 60% of recycled glass content. In terms of usage, fiberglass is commonly used in interior walls and ceilings. It is available in loose-fill, batts, and rolls, as well as boards.

But what makes fiberglass unique?

  • Accessibility. Fiberglass, since it is made from combining different synthetic materials that are easy to acquire, is the easiest to produce and therefore has a constant supply. Accordingly, this makes it the easiest insulation material to find on the market.
  • Cost-effective. Fiberglass is generally cheaper compared to other insulation materials. Its batts and rolls, for example, range between $0.64 and $1.19 (including installation) while loose-fill costs around $1 to $1.50 per square foot.
  • Easy to install. Because fiberglass is physically elastic and lightweight, it is easy to shape and install on almost all surfaces. It is especially true in areas with irregular shapes such as curved walls and domes. 

Rockwool Mineral Wool: What You Should Know

Often made of either silica or stone, mineral wool is an inorganic and non-metallic material produced by carefully combining several raw materials which are heated at a high temperature until liquified. The byproduct is then spun and shaped into a fibrous and soft mat. The process is virtually similar to how fiberglass is made. 

Mineral wool is an extremely versatile material that has superior thermal, acoustic, and even fire resistance. These characteristics, according to Mineral Wool Insulation Manufacturers Association, are mainly because of the material’s static chemical composition. The fibers of the wool-like mat also help block the movement of air.

Mineral wool can be produced with varying levels of density. and formed in different shapes. And just like fiberglass, it is available in the forms of batts and rolls as well as loose fill.

Furthermore, there are two types of mineral wool available in the market today: slag and rock wool. And for this very reason, homeowners often used the terms rock wool and mineral wool interchangeably. 

But do take note that slag and rock wool are all different (which I will elaborate in the next section), particularly in terms of their properties. 

Here’s what makes mineral wool insulation unique:

  • Passive fire protection. Mineral wool is mainly made of aluminosilicate rock like basalt, which means it is highly resistant to fire and will melt only at a temperature exceeding 2,000 Fahrenheit. Most mineral wool insulation products meet ASTM E 136 and NFPA 220 standards tests and methods too. In fact, it is under Class A products, per ASTM E 84 and NFPA 101. 
  • Excellent thermal performance. Mineral wool’s R-Value reaches up to 3.0 to 3.3 per inch of thickness. According to MIMA, it is due to the material’s ability to block and entrap air movement using its open-cell, wooly material. The material itself serves as a physical barrier to the radiative process too. 

The Difference Between Rockwool and Rock Wool?

At some point, you may get confused to find that articles that tackle “mineral wool” use the term Rockwool or rock wool. 

These terms are pretty similar and therefore often used interchangeably by homeowners and even professional builders. 

However, by definition, these three are different.

Mineral wool, as we mentioned, is a type of fiber insulation, a non-metallic and inorganic material made in several densities by combining several raw materials. There are two types of mineral wool: rock wool and slag wool.

Rock wool, also commonly referred to as stone wool, is one of the most common types of mineral wool with natural stone as one of its core elements.

Rockwool or ROCKWOOL is a company and the world’s largest producer of mineral wool. They produce the ROCKWOOL stone wool insulation that, when compared to generic stone wool insulation, is denser, more resistant to fire, has a lower water absorption rate and is more durable. 

The Difference Between Slag and Rock Wool

You probably heard of slag and rock wool and thought it is the same as mineral wool. While that is true—which leads homeowners and builders to use both terms interchangeably—these are two varying mineral wool insulation materials.

Here’s how:

  • Rockwool Insulation. Rock wool, also referred to as mineral wool, is an insulation material that is made from fibers of aluminosilicate rock—basalt, usually. It is combined with other raw materials such as dolomite or limestone and blast furnace slag. A standard rock wool insulation is composed of 70 to 75 percent natural rock while the remaining volume is blast furnace slag.
  • Slag Wool Insulation. Slag wool, on the other hand, is primarily made from fibers of molten iron ore waste. It is then mixed with blast furnace slag and some natural rock. And unlike rock wool, slag wool uses up to 70 percent of blast furnace slag while the remaining 30 percent is natural rock.  

All in all, slag and rock wool are insulation materials that are composed of basically the same materials. Both materials are produced in the same manner too. The only difference is the primary element used, which is basalt for rock wool and iron ore waste for slag wool.

 Aside from that, both materials’ components yield almost the same performance. In other words, both can provide excellent thermal performance, sound absorption, and fire protection. 

Fiberglass vs. Mineral Wool: Which is Better?

Rockwool vs Fiberglass: Installation

Mineral wool and fiberglass are both easy to install, yet fiberglass is a bit easier.

Fiberglass is relatively lower in terms of density which means it is much more versatile compared to mineral wool. Physically, it is malleable and light, making it easier to cut and fit in almost all shapes of surfaces. And as mentioned, it is excellent in uneven areas.

Mineral wool, on the flip side, is easy to trim and shape as well. The only catch is that it is heavier and denser compared to fiberglass. It needs more effort to install. 

Rockwool vs. Fiberglass: Insulation Types and Form-Factors

Fiberglass and mineral wool come in varying forms. Fiberglass is available as loose-fill or blown-in, batts and rolls, and boards. Mineral wool, on the other hand, is available as boards as well as batts and rolls.

  • Batts and rolls. Also known as blanket insulation, is the most widely available and used insulation material across the US today. It is composed of fibers and is wool-like in appearance. Both fiberglass and rock wool are available as batts and roll insulation.
  • Loose-fill. Loose fill is composed of small fiber particles, foam, and other synthetic materials. These small elements make the material easy to conform on any surface and area, including uneven ones, without disturbing finishes or structures. Loose-fill insulation is typically available in fiberglass and cellulose.
  • Rigid boards. Though it is rare, some homeowners use rigid boards. It is a rigid panel of insulation that is very effective for exterior and interior (for basements) walls sheathing.
  • Tape. Fiberglass is also available in tapes that are used for insulating pipes and joints. Tapes are essentially texturized and reinforced woven textiles.

Rockwool vs Fiberglass: R Value

In insulation, a material’s R-Value determines its ability to resist heat flow. And the greater the R-Value is, the better is the material’s thermal efficiency. 

Mineral wool insulation provides better thermal performance than any form of fiberglass.

Mineral wool’s R-Value reaches up to 3.0 to 3.3 per inch of thickness. According to MIMA, it is essentially due to the material’s prevention of convection. It blocks and entraps the movement of air using its open-cell, wooly material. The material itself serves as a physical barrier to the radiative process.

On the other hand, fiberglass’ R-Value depends on the insulation type. If it is loose fill, the thermal performance ranges between 2.2 and 2.9 per inch of thickness while batts and rolls start at 2.9 per inch of thickness. Although there are manufacturers now that produce fiberglass batts and rolls with higher density and R-Value. 

Rockwool Mineral Wool vs Fiberglass: Costs

The price of mineral wool and fiberglass depends on the type of insulation. In general, fiberglass is relatively cheaper than mineral wool. But to ask whether which is cost-effective, mineral wool gets the upper hand. 

Here’s a brief explanation of how the two differ when it comes to prices.  

  • Fiberglass. The average price of fiberglass insulation, including installation cost, ranges between $0.40 and $1.50 per square foot. The blown-in insulation material, however, is a bit higher. It costs around $1 to $1.50 per square foot. But in general, fiberglass is the cheapest insulation product available on the market today. 
  • Mineral wool. Mineral wool, on the other hand, is estimated to be 25 percent more expensive than fiberglass. Its median price ranges between $1.40 to $4 per square foot, including installation cost. 

Rockwool vs Fiberglass: Safety

Fiberglass and rock wool are tested and proven safe to install and use. According to North American Insulation Manufacturers Association NAIMA, both insulation products are the most thoroughly researched materials in terms of safety in the market today. Both mineral wool and fiberglass are composed of man-made vitreous fibers and are safe to fabricate, manufacture, install, and use.

Apart from that, mineral wool is highly resistant to bacteria, fungi, and mold as well since it is made of inorganic elements. 

Mineral Wool vs Fiberglass: Fire Resistance

While both are non-combustible materials and have high resistance to fire, mineral wool’s components can inherently reduce and delay—if not completely stop—the spread of fire. In fact, mineral wool is used as passive fire protection in many buildings. 

Take rock wool as an example. The material, which is mainly made of aluminosilicate rock like basalt, can resist and will melt only at a temperature exceeding 2,000 Fahrenheit. Most mineral wool insulation products meet ASTM E 136 and NFPA 220 standards tests and methods. It is under Class A products too, per ASTM E 84 and NFPA 101. 

The same goes with slag wool. 

Fiberglass, on the other hand, is also fire resistant but not as good as rock wool as it melts when temperature reaches 1,100 Fahrenheit. 

Mineral Wool vs Fiberglass: Common Applications

Fiberglass gets the upper hand in terms of usability. As mentioned, it is physically elastic and light and therefore fits on almost all surfaces, including uneven areas. Fiberglass is commonly used to insulate exterior and interior walls, ceilings, basements, garages and attics. Loose-fill fiberglass fits well in narrow areas such as beams, studs, and rim joists too. It is also an excellent insulation material for building wall cavities. 

Mineral wool, on the flip side, is extremely flexible in terms of usage. It can be used for residential, commercial, and even industrial buildings. For house insulation, however, it is commonly used in areas like the exterior walls and heated crawl spaces. 

Mineral Wool or Rockwool vs Fiberglass: Sound Proofing

Insulation materials are excellent in terms of soundproofing too. And while both mineral wool and fiberglass can help block and reduce outside and inside noise, the former provides better acoustic insulation.

Per MIMA, porous materials like mineral wool can help control and lessen noise by trapping the air’s movement using its fibrous texture. The friction between the narrow airways and the air particles as they move into the material causes the sound to dissipate. 

Which Is Better: Mineral Wool or Fiberglass?

Still not sure which one to choose?

Here’s a brief chart comparison.

FeaturesFiberglassMineral Wool
Thermal PerformanceR-Value ranges between 2.2 and 2.9 per inch of thicknessR-Value ranges between 3.0 and 3.3 per inch of thickness
Fire ResistanceNon-combustibleNon-combustible
Moisture ControlUnfacedUnfaced
ApplicationUsed to insulate exterior and interior walls, ceilings, basements, garages and atticsUsed in areas like the exterior walls and heated crawl spaces
ManageabilityEasy and versatileEasy yet slightly rigid
AccessibilityEasy to accessEasy to access

All in all, selecting which one to use depends on your budget as well as your preferences in terms of efficiency. If, say, you are on a budget, then it is best to opt for fiberglass insulation as both the product and the installation cost are cheaper compared to mineral wool. However, if you prefer high efficiency, then mineral wool is the best option. It is particularly true for commercial spaces. 


  • Mineral Wool Insulation Manufacturers Association at mima.info
  • Rockwool at rockwool.com
  • North American Insulation Manufacturers Association at insulationinstitute.org

Justin's been in construction for over 20 years in both new build and renovation. With experience in both commercial and residential construction, he specializes in healthier and more energy-efficient homes.