Rockwool vs Fiberglass: Which Insulation Is Better?

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As the two most popular materials used for home insulation, it should be no surprise that rockwool and fiberglass are very good at preventing temperature leakage, which is measured with something called the R-value. 

Since insulation batts are sold based on the R-value that they provide, a reliable way to measure the insulating ability of these materials is by noting the R values that they achieve at a specific thickness.

Given a benchmark thickness of 3.5 inches, a batt of Rockwool achieves an R-15 insulation value while fiberglass achieves an R-13 value, giving Rockwool about 15% better insulating ability over fiberglass at the same thickness.

Since insulators are, by nature, able to resist the flow of heat going through them, they should also have some ability to resist fire. Although there are some insulators out there (particularly cellulose) that are susceptible to igniting, both Rockwool and fiberglass have great fire resistance as both are non-combustible. 

However, Rockwool insulation gains further points here thanks to its mineral-based construction, which gives it a much higher melting point than fiberglass.

Of course, homes have to deal with a lot more than just heat&#;during the colder and rainier parts of the year, the main issue instead becomes moisture, excessive amounts of which can damage the insulation or the surrounding frame. 

Thankfully, both Rockwool and fiberglass insulation have good resistance to water damage, which can even be improved further if you buy faced insulation, which includes a layer of foil or a paper-like material on the outer layer to serve as a sort of vapor barrier.

It should also be noted that the higher density of Rockwool insulation can make it more resistant to moisture buildup as there are fewer pockets of air inside the batt for moisture to occupy.

Although they are not and should not be your first priority when shopping for insulation, having resistance to other things is still generally nice to have.

For home insulation, there are some things you would want to take into consideration&#;specifically that of insect, mold, and mildew resistance. 

Generally, though, you can freely pick either of the two for this metric; both fiberglass and Rockwool insulation are inorganic materials that don&#;t contribute to (and even suppress) the invasion of fungi and insects within the walls they occupy. 

(Just for reference, cellulose insulation is an organic material, which means fungi and insects can feed on it if it is not given any additional treatment.)

Another consequence of the way insulation works is that it can also provide some level of acoustic deadening (which is distinctly different from soundproofing, as they do not provide full soundproofing).

While some sources will tell you that Rockwool provides better acoustic deadening than fiberglass, this is actually not true in all cases because of how sound and sound deadening works.

Now, we&#;ll spare you the complicated science that goes on behind the scenes and give you the summary. 

When it comes to sound deadening, the higher density of Rockwool insulation makes it good at blocking out lower-frequency noises like heavy thuds. Meanwhile, higher-frequency noises like claps are better blocked out by the looser composition of fiberglass insulation batts.

Now, it is one thing for insulation to perform better than its competitor; however, all of its advantages become immediately irrelevant when the insulation can&#;t be installed in the first place.

And it is here that we find one of the reasons behind the popularity of fiberglass in homes&#;since they are much lighter and less dense than Rockwool by volume, fiberglass is much easier to install. 

Fiberglass is pliable enough to be worked around difficult spaces, such as around pipes and in crawl spaces, and batts of the stuff could also be easily cut to fit specific sizes and shapes. 

By contrast, Rockwool insulation batts are a lot more rigid, owing to their density, which makes them more suited to spaces with fixed shapes so they don&#;t have to be cut or bent at great effort.

When it comes to insulating products, their warranty is usually treated like that of any other product&#;most manufacturers will have a 1- to 3-year warranty against production defects on their insulation batts.

Of course, longevity is a very different&#;but very important&#;quality you will need to take into consideration. 

Based on our experience and analysis, the typical lifespan of Rockwool insulation is about 30 years before they will need to be replaced. By comparison, fiberglass is generally expected to last for about 25 years; however, fiberglass insulation can and does collapse and flatten over time, which can lower its insulating ability faster than Rockwool.

Last but definitely not the least of your concerns is the cost of having either as your home insulation.

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Depending on where you source your insulation batts and the pricing of your contractor (which itself can vary by a significant margin depending on their skill level and the complexity of the project), Rockwool is generally more expensive than fiberglass.

Gathering info from various retailers and contractors, you can expect to pay about $0.50 to $0.60 to install one square foot of fiberglass, while Rockwool costs about $0.60 to $0.75 per square foot&#;a cost difference of up to 25% per square foot.

When it comes to insulating products, their warranty is usually treated like that of any other product&#;most manufacturers will have a 1- to 3-year warranty against production defects on their insulation batts.

Of course, longevity is a very different&#;but very important&#;quality you will need to take into consideration. 

Based on our experience and analysis, the typical lifespan of Rockwool insulation is about 30 years before they will need to be replaced. By comparison, fiberglass is generally expected to last for about 25 years; however, fiberglass insulation can and does collapse and flatten over time, which can lower its insulating ability faster than Rockwool.

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Fiberglass insulation has long been a popular option for slowing the transmission of heat through the walls and ceilings of a home. While it may have the added benefit of creating a fire-resistant layer between the interior and exterior walls, fiberglass still may not measure up to the natural abilities of Rockwool. Like fiberglass, Rockwool is an insulation material that is regularly used in residential, commercial, and industrial buildings.

However, Rockwool can be differentiated from fiberglass by comparing the heat retention, fire resistance, moisture resistance, and soundproofing capabilities. Keep reading to find out more about Rockwool insulation.

1. Rockwool is made of rocks heated to become lava-like liquid.

The process by which Rockwool insulation is made helps to explain the true fire-resistant potential of this product. It&#;s composed primarily of basalt rock and a recycled steel-making byproduct known as slag. These components are superheated, allowing them to liquefy and mix together into a lava-like liquid. In order to melt these substances, the temperatures must exceed 2,900 degrees Fahrenheit.

The mixture is then blown into a large spinning chamber designed to stretch the superheated liquid into fibers. These fibers are then gathered together and compressed into a mat, which can be cut into slabs of Rockwool insulation.

By creating Rockwool through this process, all organic matter is eliminated, greatly increasing the mold- and mildew-resistance of the finished product.

2. It contains between 16 to 75 percent recycled material.

The confusion about the amount of recycled material used to make Rockwool insulation can mostly be attributed to the statistics about mineral wool insulation in general. Rockwool is a brand-specific type of mineral wool insulation that is so popular the name became synonymous with the appropriate term, which is mineral wool. The brand-specific Rockwool insulation is typically made of between 16 to 40 percent recycled materials, according to the manufacturer. However, the U.S. Department of Energy has stated mineral wool insulation contains an average of 75 percent of recycled materials.

This estimate is hard to back up because the Department of Energy makes the distinction between standard &#;rock wool&#; insulation and &#;slag wool&#; insulation, but doesn&#;t note the difference in the amount of recycled material for each product. Also, this is a perfect example of the &#;Rockwool&#; brand name being used in place of the generic material name, blurring the lines between products.

In general, it can be derived that the amount of recycled material in Rockwool insulation is not precise because it ultimately depends on the specific product. Standard Rockwool insulation may only have between 16 to 40 percent recycled material, while slag Rockwool insulation can be made with up to 75 percent recycled material.

3. Rockwool has excellent heat retention.

Both fiberglass and Rockwool are effective at keeping a home cool in the summer and warm in the winter, but the specific thermal efficiency of these materials favors Rockwool. While fiberglass insulation is capable of offering an R-value of about 2.2 to 2.7 per inch of insulation, Rockwool has an R-value between 3.0 to 3.3 per inch of insulation.

Fiberglass insulation also tends to lose its thermal efficiency over several years as it begins to degrade. Due to the method of construction and the materials used to make Rockwool insulation, the thermal performance of this insulation remains stable over the lifetime of the building. However, Rockwool tends to cost more per square foot than fiberglass insulation.

4. The material is fire-resistant up to 1,400 degrees Fahrenheit.

As noted previously, Rockwool insulation is formed from literal rocks and steel slag that must be heated beyond 2,900 degrees Fahrenheit in order to mix the component materials and create this highly effective insulation. With this in mind, it makes sense that mineral wool products in general can resist fire, flames, and heat up to 1,400 degrees Fahrenheit, while some Rockwool products are capable of resisting temperatures up to 2,150 degrees Fahrenheit without melting, smoking, or catching on fire.

This impressive heat-resistance is ideal for building homes because the insulation forms a fire-resistant barrier between the interior and exterior of the home, between rooms, and even between floors, slowing the spread of fire. It should be noted that fiberglass insulation is also highly heat-resistant, though it begins to melt at about 1,100 degrees Fahrenheit.

5. Rockwool is a highly durable insulation option.

The durability of this insulation material is difficult to dispute, given that it is capable of retaining its thermal efficiency over several decades with minimal degradation in its R-value. This is primarily due to the materials used to make Rockwool insulation, including rock and steel slag, which are known for having a high level of durability and natural resistance to decay and corrosion.

However, the durability of Rockwool isn&#;t limited to the heat retention quality of the material. The impressive water-resistance, mold-resistance, mildew-resistance, and fire-resistance also contribute to the durability and capability of Rockwool insulation. This is especially true of the material&#;s moisture-resistant qualities, without which the insulation could absorb and retain water from highly humid air, causing the premature breakdown of the material.

6. Rockwool insulation is great for soundproofing rooms.

Some people may not appreciate the heftiness of Rockwool insulation because it does tend to be thicker than fiberglass insulation, but this helps to slow the transmission of heat and it has the added effect of slowing sound waves. As sound waves attempt to move through the material, they are slowed and sometimes completely blocked, creating built-in soundproofing.

While the thickness of the insulation helps to block noise, it is the density of Rockwool insulation that provides the soundproofing. Fiberglass insulation has a density of about 0.5 to 1.0 pounds per cubic foot, allowing it to reduce sound by 4 to 10 decibels. Rockwool insulation has a density of around 1.7 pounds per cubic foot, which is capable of consistently dampening sound by 10 to 15 decibels.

7. Rockwool allows moisture to escape and prevents the growth of mold.

The construction and composition of Rockwool makes it ideal for rooms that are prone to high levels of humidity, like the bathroom or kitchen. Rockwool insulation&#;s moisture-resistant and vapor-permeable qualities mean that any liquid water will drain away from the insulation instead of soaking into it, while gaseous water vapor will pass through without dampening the material.

Additionally, Rockwool insulation is inorganic, so it makes a poor medium for mold and mildew to grow as there is nothing for them to use for energy. In fact, Rockwool products are also tested and certified as resistant to fungal growth, reducing the chance that users will open up the wall and find a dangerous biological problem waiting for them.

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