Mineral Wool vs. Fiberglass Insulation: Pros, Cons, and Costs

Mineral wool insulation versus fiberglass is a common debate among homeowners regarding insulating a home and adding soundproofing panels. While mineral wool and fiberglass dramatically climbed the popularity ladder after the rise in awareness of insulation health hazards and asbestos, there are some essential factors to consider not just for your home but for your health.

Knowing the key differences between these types of insulations can help you decide which one is best for you and your next project. 

Key Differences Between Fiberglass and Mineral Wool Insulation

Now let’s compare the main differences between fiberglass and mineral wool insulation. Fiberglass and mineral wool—also commonly called Rockwool—are both popular insulation materials but differ in composition, installation, and performance. Fiberglass insulation is made from melted glass fibers, providing strong thermal resistance, and is often less expensive, making it a budget-friendly option. It’s lightweight, easy to install, and widely available in batt or loose-fill forms. A word of warning—fiberglass can irritate the skin and respiratory system, requiring protective gear during installation.

Mineral wool, on the other hand, is made from natural stone or industrial slag, making it denser and more durable than fiberglass. This density gives it superior soundproofing qualities and higher resistance to fire and water, making it ideal for areas needing added protection, like basements. However, due to its weight and density, mineral wool tends to be more expensive and can be more challenging to install.

What Is Mineral Wool Insulation?

Rockwool is also known as mineral wool due to its fibrous nature. It’s a more eco-friendly option than fiberglass, as manufacturers make it using natural and recycled materials.

Rockwool’s base is volcanic-rock basalt—heated to a scorching 3,000 degrees Fahrenheit until it liquefies—then mixed with slag, a by-product from steel that generally ends up in landfills. The resulting mixture is then spun into threads and flattened with a hydraulic press. 

Best for: Homes needing extra soundproofing, fire resistance, and moisture protection as well as basements, attics, and exterior walls where durability and added safety features are priorities.

Pros of Rockwool Insulation

Rockwool insulation offers a range of benefits, making it a popular choice for homeowners prioritizing performance and durability. Its high density makes it excellent for soundproofing, ideal for reducing noise between rooms or within multi-family buildings. 

Rockwool is also highly durable, withstanding the test of time in more demanding applications like basements or exterior walls. It’s straightforward to install, making it a convenient option for professionals and experienced DIYers. 

If you live in a fire-prone area, you will appreciate that Rockwool’s fire-resistant properties add an extra layer of safety, while its water-resistant composition helps prevent mold and moisture issues. These qualities make Rockwool a versatile, resilient choice for many home insulation needs.

Cons of Rockwool Insulation

Rockwool insulation tends to be more expensive than other insulation options, which may be a consideration for budget-conscious homeowners. 

Rockwool also has a higher pH level which can make it unsuitable for certain environments, especially where chemical sensitivity is a concern. It’s also not biodegradable, which may be a drawback for those seeking environmentally friendly materials. 

Most importantly—Rockwool can pose health risks during installation, as its fibers can irritate the skin, eyes, and respiratory system, requiring protective gear and careful handling.

What Is Fiberglass Insulation?

The invention of fiberglass insulation started as an accident in the 1930s. Using a high-pressure jet system to vacuum seal glass blocks resulted in thin, fiber-like glass threads. 

To create the fiber-like threads of glass, producers heat the glass to extreme temperatures and then compress it to form long rolls or blankets. Since manufacturers make this insulation from glass, it's not as eco-friendly as mineral wool. However, it is biodegradable. 

Best for: Homes in moderate climates where cost-effectiveness is essential as well as single-family homes, new constructions, and areas that experience extreme weather conditions. 

Pros of Fiberglass Insulation 

One of the primary benefits of fiberglass insulation is affordability. As an added benefit, fiberglass is fire-resistant, enhancing safety in residential settings. Its ease of installation is also another significant advantage. 

Fiberglass insulation also performs well against extreme weather conditions, ensuring comfort throughout the year. One of the main appeals for many homeowners is how low maintenance this material is, requiring very little maintenance after installation.

Cons of Fiberglass Insulation

While fiberglass insulation offers numerous benefits, it also has several drawbacks that homeowners should consider. One significant limitation is its lack of water resistance, which may lead to potential issues in damp environments, such as mold growth. 

Another safety concern is that fiberglass particles can be hazardous for asthmatic individuals. The particles can become trapped in the airway and cause excessive sneezing and coughing. In some cases, fiberglass insulation may require covering to minimize exposure to these particles, adding an extra step during installation. Fiberglass also lacks breathability, which can hinder moisture regulation within walls, potentially leading to further complications.

Fiberglass vs. Mineral Wood Insulation: Every Characteristic, Compared

Both are easy to install and require that you wear protective gear, such as goggles, gloves, and a mask. Considering both have pros and cons, here are the key differences to consider when choosing the best insulation. 

R-Value: Mineral Wool 

A critical factor for selecting insulation is the R-value, which represents heat resistance. The lower the R-value, the less heat the insulation blocks. If you’re wondering, what R-value do I need, you need to crunch some numbers.

Not sure how to calculate R-value? Rockwool has an R-value between 3 to 3 1/3 per inch, while fiberglass has an R-value between 2 1/5  to 2 7/10 per inch. For example, if you buy mineral wool insulation that is 3 inches thick, multiply it by three for an approximate R-value of R6. 

When choosing R-values, a higher R-value is essential if you're looking for ways to keep your utility bills down by better regulating heat flow in your home. R-values can range from R10 for floor insulation and up to R60 for attics. 

While mineral wool may seem like the better insulation, you may also need to consider your location to determine what R-value is best for your home. For example, Energy Star provides R-value recommendations for various places in the country, so you may not need to invest in mineral wool. 

Ease of Installation: Tie

The good news is that both mineral wool and fiberglass are easy to install. It just depends on your preference.

You can purchase mineral wool and fiberglass in batts, rolls, and blankets and trim them according to your needs. You can also blow mineral wool and fiberglass, which is perfect for tricky spots or tight corners. You can spray in the insulation instead of paying for an entire blanket. 

You may wonder: who installs insulation? If you’d rather leave this job to a pro, call an insulation company near you to help you choose the type of insulation and the R-value. 

Soundproofing: Mineral Wool 

The higher the density of the insulation, the better it will block sounds. Since mineral wool is thicker than fiberglass, it’s usually the best choice if soundproofing a room is one of your top priorities. 

For the best results, look for high-performance mineral wool, which has double the density of regular mineral wool and can absorb sounds. If you use fiberglass insulation, you'll have some sound absorption, but it probably won't measure up to mineral wool. 

Cost: Fiberglass 

If budget is a significant factor in your decision, fiberglass is friendlier for your wallet. Fiberglass usually costs about $0.50 per square foot, while on the other hand, mineral wool costs about $0.62 per square foot. If you’re looking for ways to reduce your utility bills in your home, mineral wool may be a better investment in the long run. 

Water Resistance: Mineral Wool 

Water resistance is significant for insulation because it prevents rotting and the eventual growth of bacteria. 

Unfortunately, fiberglass is not water-resistant like mineral wool. Fiberglass insulation will absorb water and become soggy, eventually leading to significant issues and its ability to insulate your home. 

Fire Resistance: Mineral Wool

Mineral wool insulation is more fire-resistant than fiberglass, capable of withstanding temperatures up to 1,800°F (982°C) due to its non-combustible composition of natural stone and recycled materials. In contrast, fiberglass insulation ignites around 1,000°F (538°C). Fire resistance is essential when choosing insulation, as it can slow the spread of flames, providing critical time for evacuation and firefighting efforts.

Thermal Drift (Longevity): Mineral Wool

Thermal drift refers to the gradual decrease in the effectiveness of insulation over time, leading to a reduction in its R-value, which measures thermal resistance. As insulation ages or is exposed to environmental factors, such as moisture and temperature fluctuations, its ability to resist heat flow diminishes, resulting in decreased energy efficiency. Choosing insulation with a lower susceptibility to thermal drift is crucial for maintaining energy efficiency and reducing heating and cooling costs over the life of a building.

Between the two, mineral wool insulation is better at resisting thermal drift than fiberglass insulation. Fiberglass is more susceptible to this phenomenon because its R-value can decline due to factors like settling or moisture absorption, leading to a loss of insulating performance over time. On the other hand, mineral wool maintains its insulating properties more effectively, largely due to its denser structure and water-resistant qualities, which help it retain its R-value.

Eco-Friendliness: Tie

While you can consider mineral wool more eco-friendly because recycled materials make up most of its composition, including leftover steel that would eventually end up in a landfill, unfortunately, it is not biodegradable like fiberglass. 

So the bad news is that mineral wool can sit in landfills for years, but the good news is that you can use it in other ways, like for hydroponics. This is a popular method of growing plants but without soil. 

After thoroughly cleaning mineral wool, it’s a great material for plants because of its spongy texture and thermal stability. You can also cut it into customized sizes based on the size of your plants. 

And while it won’t harm the environment, fiberglass can cause health issues, such as skin and eye irritation and breathing problems. Therefore, it's always critical to protect yourself when handling fiberglass insulation, such as wearing gloves, a long-sleeve shirt, a mask, a pair of goggles, and working in a ventilated area.