Rockwool vs. Fiberglass Insulation: What’s the Difference?

Carrie Circosta
Written by Carrie Circosta
Updated November 16, 2022
Woman sitting on bed is holding her dog
Photo: Westend61 / Getty Images


  • Know the proper R-value for your home when choosing insulation. 

  • Rockwool is eco-friendly, while fiberglass is biodegradable. 

  • Fiberglass is less expensive, but Rockwool could lower utility bills.

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Rockwool vs. fiberglass insulation is a widespread debate among homeowners regarding insulating a home and adding soundproofing panels. While Rockwool 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 two materials can help you decide which one is best for you and your next project. 

Rockwool Insulation Pros and Cons

Handyman installing mineral wool floor insulation
Photo: SerhiiKrot / iStock / Getty Images Plus

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. 

Pros of Rockwool Insulation

  • Highly dense 

  • Great for soundproofing 

  • More durable

  • Easy to install 

  • Fire-resistant 

  • Water-resistant 

Cons of Rockwool Insulation

  • More expensive 

  • Higher pH level

  • Not biodegradable 

  • Potential health hazards, such as skin and eye irritation and difficulty breathing for certain individuals

Fiberglass Insulation Pros and Cons

Fiberglass insulation installed in the attic
Photo: Colin & Linda McKie / Adobe Stock

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 Rockwool. However, it is biodegradable. 

Pros of Fiberglass Insulation 

  • Inexpensive 

  • Fire-resistant 

  • Easy to install 

  • Holds up against extreme weather conditions 

  • Low maintenance 

Cons of Fiberglass Insulation

  • Not water-resistant 

  • Hazardous for asthmatic individuals as fiberglass particles can get trapped in the airway and cause excessive sneezing and coughing 

  • May require covering, depending on where you install it, to reduce exposure to fiberglass particles

  • Lacks breathability 

Rockwool vs. Fiberglass Insulation

Visual comparison of rockwool and fiberglass insulation, with rockwool having a rough, tighter compaction and fiberglass being looser layered and fluffy
Photo: Bohdan / Adobe Stock, Kellis / Adobe Stock

Both Rockwool and fiberglass 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. 


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. 

Rockwool typically 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 Rockwool 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 Rockwool 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 Rockwool. 

Winner: Rockwool

Ease of Installation

Worker installing rockwool insulation on the floor
Photo: brizmaker / iStock / Getty Images Plus

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

You can purchase both Rockwool and fiberglass in batts, rolls, and blankets and then trim them based on your needs. You can also blow Rockwool and fiberglass, which is perfect for tricky spots or tight corners. You can spray in the insulation instead of paying for an entire blanket. 

If you’d rather leave this job to a pro, call an insulation contractor who can help you choose the type of insulation and the R-value. 

Winner: Tie


The higher density the insulation has, the better it will be at blocking sounds. Since Rockwool is thicker than fiberglass, it’s usually the best choice if soundproofing is one of your top priorities. 

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

Winner: Rockwool


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, Rockwool costs about $0.62 per square foot. If you’re looking for ways to reduce your utility bills in your home, Rockwool may be a better investment in the long run. 

Winner: Fiberglass


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

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

Winner: Rockwool

Eco-Friendliness and Sustainability​

While you can consider Rockwool 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 Rockwool 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 Rockwool, 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. 

Winner: Tie

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