Batts of mineral wool insulation stacked together

High-quality insulation can help keep your home comfortable and your energy bills low, all while minimizing your carbon footprint. The importance of effectively insulating your living space cannot be overstated. 

While many homeowners are familiar with fiberglass and cellulose insulation, a new type of insulating material has recently been gaining popularity among architects, builders, and homeowners alike.

Rockwool insulation is a material that offers excellent durability, high R-values, and environmental sustainability.

What is the R-Value of Rockwool Insulation?

Rockwool or mineral wool insulation offers an R-value of 3.0 to 3.3 per inch of thickness. While it costs slightly more than other common insulating materials like fiberglass and cellulose, it provides far greater thermal efficiency, heat retention, moisture resistance, and sound-dampening capabilities. 

The thermal insulation performance does not degrade over time and will usually remain stable throughout the entire lifespan of the building. This longevity is because it is made from liquified natural rock, one of the toughest substances on earth. 

Here is a table summarizing the R-values of Rockwool insulation based on thickness:

Rockwool Insulation Thickness (Inches)R-Value
1R3.0 to R3.3
2.5R8 to R10
3.5R13 to R15
5.5R21 to R23

Let’s learn some more about mineral wool and how it’s made so you can determine if you want this insulating material installed in your home. 

Factors Influencing the R-Value of Rockwool Insulation

You may have noticed that we give the R-value of Rockwool insulation in terms of ranges instead of a fixed value. This is because R-values of insulation materials, including Rockwool, are affected by various factors. 

Knowing the factors influencing the R-values of Rockwool insulation will help you choose the best option for your home. These factors include:

Material Thickness

This is the primary factor affecting the R-value of Rockwool insulation. Generally, thicker insulation provides better thermal resistance.

The R-value is typically measured per inch of material, so the more inches you have, the higher the overall R-value.


The density of Rockwool insulation ranges between 25 and 200 kg/m³. This variation impacts the material’s R-value.

Higher-density insulation materials often have a higher R-value because they contain more fibers, reducing air gaps and enhancing thermal insulation.


Compressing Rockwool insulation reduces its R-value. This points back to the thickness factor. When you compress this material, you get fewer inches of insulation thickness, lowering its R-value.

Consequently, it’s recommended to install Rockwool insulation without compressing to maintain its thermal performance.

Thermal Bridging

Incomplete or ineffective coverage of Rockwool insulation can lead to thermal bridging. As a result, heat can easily escape through structural elements or other uninsulated areas, lowering the insulation’s effectiveness.

Installation Quality

The quality of installation is essential for maximizing the R-value of Rockwool insulation. Gaps, voids, and improper installation can lead to heat loss and reduced thermal performance.

A rule of thumb is to follow manufacturer installation guidelines for optimal results.

An end-facing view of a roll of mineral wool insulation
Making Rockwool starts with superheating natural rock until it becomes molten.

Rockwool Insulation – Manufacturing Process

The process by which Rockwool insulation is manufactured is quite unique and fascinating. Read on for a step-by-step breakdown of this unique manufacturing process.

Materials Used:

Rockwool insulation is made primarily from natural rock that has been heated at temperatures of over 3,000°F (1,648.89℃). To be precise, basalt rock and slag are (usually) the two main components used. 

Basalt is a common volcanic or igneous rock, while slag is essentially a recycled byproduct of steel production. Together, these components form one of the sturdiest insulating materials currently available.

Heating and Melting:

Before the basalt rock and steel byproduct can be combined to form the insulation, each material needs to be individually heated and melted. However, this is no easy task.

The rock and slag are heated in a furnace at temperatures exceeding 2,900°F (1,593.33℃) until both have been melted into a lava-like liquid. 

The liquified materials are then mixed and transferred to a special spinning machine or chamber.  

Spinning Chamber:

The liquified slag and basalt rock take on a magma-like texture, at which point they must be exposed to a high-pressure jet of steam or air. Once treated with high-pressure steam, the liquid is blown into a giant spinning chamber.

This chamber is designed to stretch the molten rock and slag into long fiber strands by spinning the magma-like substance at super-high speeds. Imagine a cotton candy machine filled with liquified rock instead of molten sugar. 

Amazing! Right? We think so as well!

The molten rock is spun centrifugally at incredible speeds until it cools and resolidifies in the form of long fiber strands. These strands are known as Rockwool

Collection and Compression:

As the molten rock and slag resolidify into long fiber strands, the spinning machine captures each strand and presses them together into a mat.

After being removed from the spinning chamber, the strands of Rockwool are further compressed into thick, dense mats, which can then be cut into conveniently sized batts of insulating material.

These slabs of insulation are later installed in buildings. You can customize the size and shape of each slab according to the needs of your home. 

Elimination of Organic Matter:

Heating natural rock until it has been liquified into a lava-like substance effectively eliminates all organic matter from the finished product. 

The lack of organic matter makes mineral wool a poor medium for the growth of mold and mildew since there is no source from which it can draw energy.

Hence, this manufacturing process significantly increases its resistance to mold, mildew, and other allergens. 

Benefits of Rockwool Insulation

The unique composition and manufacturing process of Rockwool produces a high-performing insulating material with numerous benefits. And now you know how it’s made, it’s time to think about whether to install it in your home. 

Here are some of the advantages of mineral wool insulation in residential spaces:

Close-up of worker hands in white gloves insulating rock wool insulation staff in wooden frame for future walls for cold barrier.
It has the properties of a highly effective agent of heat retention.

High R-value and Heat Retention

Rockwool is essentially a mass of fine, intertwined fibers, each with a diameter of around 3-4 micrometers. This intertwined structure allows the insulation to trap the air that passes through it.

The fibers often contain a binder and some oil to minimize dusting, slowing the heat transfer and increasing retention capacity. Binders increase the R-value of the insulation and provide it with greater insulation capabilities. 

With an average R-value of 23, mineral wool insulation can help keep your living space at a comfortable and consistent temperature without adjusting the thermostat so often. The thermal performance of this material has also remained stable over the years. 

Here’s a chart showing the R-values of other insulating materials compared to Rockwool:

Insulating MaterialR-Value
Rockwool3.0 to 3.3 per inch of insulating material
Fiberglass2.2 to 2.7 per inch.
CelluloseBetween 3.2 and 4.0 per inch of thickness
Foam BoardUp to 5.0 per inch

Sustainable, Recyclable Components

Rockwool insulation is constructed from sustainable and eco-friendly materials like natural rock and steam and is as good for the planet as it is for your home.

Even the slag used in the manufacturing process is a recycled byproduct of the steel industry. 

In fact, according to figures released by the US Department of Energy, some varieties may contain as much as 75 percent post-industrial recycled material.

Click here to learn more about the sustainable building materials currently changing the real estate market.

All forms of mineral wool will contain anywhere between 16 and 75 percent recycled material, but the exact amount might vary depending on the product.

Consult your architect or builder if you want to purchase mineral wool insulation with a higher level of recycled content. 

Safety and Fire Resistance

Rockwool insulation is non-combustible and incredibly heat-resistant. The components of mineral wool – such as basalt volcanic rock and steel slag – need to be heated beyond 2,900°F (1,593.33℃) before they can be melted and mixed to create the finished product. 

It makes sense, therefore, that mineral wool can resist fire and heat up to a temperature of 1,400°F (760℃). In other words, the material won’t melt or catch on fire until the temperature exceeds 1,400°F (760℃), although some varieties are known to be heat-resistant up to 2,150°F (1,176.67℃).

The fire-resistant qualities of mineral wool have made it the ideal insulating material to be used as a fire stop between the different floors of a house.

Click here to learn more about the fire-resistant properties of various insulating materials. 

Using mineral wool as a firestop between floors is required by the building code of many zoning districts in the US.

You can ask your local building inspector to help you identify the parts of your house that most require mineral wool firestops. These are ideal for fire protection at any moment.

Moisture-Resistant and Hypoallergenic

As a material, Rockwool is highly water-repellent. It is also quite vapor-permeable, meaning it does not trap moisture and allows it to escape into the air. This makes it the perfect insulation material for the parts of the house that are prone to extreme humidity, such as the kitchen and the bathroom. 

Any liquid water that comes into contact with the material drains away without being absorbed into the material.

Water vapor can also easily pass through mineral wool insulation without dampening the material. Moreover, the manufacturing process of Rockwool insulation effectively eliminates any organic matter. 

These factors ensure stone wool insulation does not promote the growth of mold, mildew, fungus, and other allergens.

Most mineral wool products are extensively tested for their resistance to fungal growth. Hence, it is one of the safest and most hypoallergenic insulation materials currently available. 

Exceptional Durability

Apart from being great for the environment and an effective form of insulation, Rockwool is also a good investment because it has the longevity to remain in your home for as long as it stands, with minimal corrosion and no decrease in insulating capability. 

In other words, the R-value of the insulation remains constant, even many decades after installation. Natural rock and steel slag are both sturdy materials and are relatively resistant to corrosion and decay.

Furthermore, as mentioned above, Rockwool is a non-organic, vapor-permeable material that does not absorb and retain moisture in humid environments.

As a result, it is not susceptible to the problems of rusting, corrosion, and premature degradation often caused by moisture. 

Ease of Installation

Rockwool insulation is straightforward to work with. Firm, dense batts of Rockwool can be easily cut with an insulation saw or a long, serrated knife rented from your local DIY outlet.

Once cut into the required shapes and sizes, batts can be friction-fit snugly into place without the need for staples. 

Mineral wool fibers are compressed so tightly together that the material can never slump down or shift out of position, which might have lowered its insulating value.

Products made from the material can also quickly fill all holes and gaps in your building envelope, leaving no opportunities for air leakage. 

The batts will not be affected by weather conditions if stored outside. Even if they get wet, the water beads will simply roll off the fibers instead of soaking in.

However, the insulation has no foil or kraft paper to act as a vapor barrier, so an independent permeable membrane might need to be installed for maximum efficiency. 

Great Soundproofing Ability

Stone wool insulation is thicker, denser, and heavier than other common types of insulating material, such as fiberglass insulation. While this might cause slight inconvenience during transportation, it also results in excellent built-in soundproofing that few other materials offer. 

The insulation batts can effectively slow the transmission of soundwaves, reducing (or sometimes wholly blocking) the unwanted noises of traffic, construction, or other activities outside your home.  

With a density of about 1.7 pounds per cubic foot, Rockwool can dampen sound by 10 to 15 decibels. The exceptional sound-deadening capability makes it the perfect insulating material for bedrooms, music studios, and media rooms. 

A man wearing a white mask and white gloves installing Rockwool mineral wool insulation in between the studs in the wall
When installing insulation, protective equipment is a must.

Tips for Installing Rockwool Insulation Effectively

Installing stone wool insulation effectively is crucial to maximizing its energy efficiency and keeping your home more comfortable. Here are some tips to get you started:

  • Safety first: Wear appropriate safety gear, including gloves, long sleeves, and safety glasses, to protect yourself from the fibers in Rockwool insulation. Consider using a dust mask for added protection.
  • Measure and Cut Precisely: Measure the spaces to be insulated carefully, and cut the Rockwool insulation batts or rolls to the appropriate size using a utility knife. Make sure the insulation fits snugly without gaps or compression.
  • Ensure Proper Ventilation: Maintain proper ventilation by installing soffit and ridge vents in your attic, which will help prevent moisture buildup and mold growth.
  • Seal Air Leaks: Before installing Rockwool insulation, check for any gaps or air leaks in the walls, ceiling, or floors. Seal these areas with caulk or weatherstripping to prevent drafts and improve energy efficiency.
  • Vapor Barrier: Depending on your climate, you may need to install a vapor barrier on the warm side of the insulation (usually the interior). This helps control moisture and prevent condensation.
  • Consider Professional Installation: If you’re unsure about how to install Rockwool insulation properly, or if you have a large and complex project, consider hiring a professional insulation contractor to ensure the job is done correctly.

Where Do You buy Rockwool (Or Mineral Wool Insulation) Anyway?

Mineral wool is pretty bulky, so it’s probably best to pick it up locally at a high-volume distributor or store.

The main two options that I can see are the Safe’ n’ Sound Rockwool product, which is a 3-inch soundproofing and fire-resistant version, and the R-15 Comfortbatt.

Amazon does have some options, but due to the shipping costs, you’ll definitely want to compare prices to the above options.

Final Thoughts

The R-value of Rockwool insulation can vary between 3.0 and 3.3 per inch of thickness. It also offers other useful features like fire resistance, moisture resistance, and soundproofing, which have made it one of the most popular types of insulating material in the US.

However, before installing Rockwool insulation in your home, you should research and consult with home improvement experts and architects in your area. 

For the ultimate insulation faceoff, you can view our comparison on Rockwool Vs. Cellulose Insulation and Fiberglass Vs. Rockwool!


  1. Hi there, I’m curious about the R- Value of mineral wool insulation in my attic. I have a older home and I’m looking to upgrade my insulation to make sure it’s energy efficient. Can you please provide more information on the R-Value and how it compares to other types of insulation? Thanks for the helpful post!

    1. Hi, thanks for the question! Without seeing it in person, maybe a starting point would be to check the depth or the insulation in inches of thickness. Then you can compare the tables (we have them on our site – you can search) for the different insulation types and the R Value per inch to see which might make sense. If you have the space in the attic, blown in fiberglass would be the easiest and cheapest option, or you can just add more mineral wool.

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