Out of the many things on the market you can buy and install to restore an older home or upgrade a younger one, insulation is the one that arguably offers the most benefits. 

Source: forbes.com

From temperature retention to sound deadening, energy efficiency, and other perks, the effects of a proper insulation upgrade make the choice to get one a no-brainer.

Rockwool and fiberglass are two of the most popular types of insulation for residential applications. Besides being generally good at doing their basic jobs, each of these insulation materials have their quirks and qualities that make them better than the other options.

We will be exploring a rockwool and fiberglass insulation in this breakdown to help you find the right insulation for your home.

Rockwool Insulation Overview

Source: rockwool.com

Rockwool is the name of a Danish manufacturer of insulating products made of mineral wool, which is the generic term for this type of product. 

Made from basalt rock that has been melted at extremely high heat (upwards of 2,000°F!) and spun into a fuzzy wool, Rockwool insulation has all of the typical hallmarks of a good home insulator along with some added perks from its unique construction, which include:

  • Excellent heat & fire resistance
  • High density and weight
  • Resistant to organic damage (mold, mildew, bugs)

Fiberglass Insulation Overview

Source: unsplash.com

The distinctly pink batts of insulation you see in most homes are made of fiberglass—and you seeing it so often is simply proof of its popularity. 

Fiberglass insulation is, like mineral wool, made from a similar process of melting down glass and spinning it at very high speeds as they cool. The resulting strands are then combined with binders to create the products that we see, which feature:

  • Available in various form factors
  • Light and flexible
  • Effective but affordable

Rockwool vs Fiberglass: Insulation Comparison

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.

Rockwool vs Fiberglass: Fire Resistance Comparison

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.

Rockwool vs Fiberglass: Moisture Resistance Comparison

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.

Rockwool vs Fiberglass: Other Resistances Comparison

Although they are not and should not be your first priority when shopping for insulation, having resistances 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.)

Rockwool vs Fiberglass: Acoustic Deadening Comparison

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.

Rockwool vs Fiberglass: Installation Comparison

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.

Rockwool vs Fiberglass: Cost Comparison

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

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.

Rockwool vs Fiberglass: Warranty Comparison

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.

Rockwool vs Fiberglass: Final Showdown

Rockwool and fiberglass are two of the most popular insulation materials for a reason—when you take everything we’ve considered from a bird’s eye view, we find that neither is completely better than the other.

If your insulation project does not involve working with irregular shapes and spaces, Rockwool provides superior insulation for longer. By contrast, fiberglass insulation is much more forgiving and can fill in and insulate spaces where Rockwool cannot.

Editorial Contributors
Matt Greenfield

Matt Greenfield

Matt Greenfield is an experienced writer specializing in home improvement topics. He has a passion for educating and empowering homeowners to make informed decisions about their properties. Matt's writing focuses on a range of topics, including windows, flooring, HVAC, and construction materials. With a background in construction and home renovation, Matt is well-versed in the latest trends and techniques in the industry. His articles offer practical advice and expert insights that help readers tackle their home improvement projects with confidence. Whether you're a DIY enthusiast or a seasoned professional, Matt's writing is sure to provide valuable guidance and inspiration.

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