Rockwool vs Fiberglass Insulation: 7 Main Differences, Pros & Cons

Rockwool and fiberglass are popular insulation materials that are typically found within walls, but are also part of many on-surface soundproofing panels. Because of their similar application, the differences can be very confusing at first.

This article will shed light on the main pros and cons of both materials, and the main differences in their features. In the end, you will know which material is best suited for your project.

What is Rockwool?

Rockwool also known as Mineral wool is a fibrous wool-like man-made fiber. As the name suggests, mineral wool is made from a naturally occurring volcanic rock basalt. It liquefies at a temperature of 3000° Fahrenheit. The next step in the process is mixing the liquified basalt with slag, a by-product of the steel manufacturing process.

The resultant compound is spun into threads and flattened out using a hydraulic press. The compressed fiber-strands are made out into batts, rolls or blankets of different dimensions. About 70%, of Rockwool is made from recycled material, making it a more eco-friendly product than Fiberglass.


  • Water retention capacity
  • Fire-resistance
  • Durable and less prone to breakdowns
  • Acts as a sound insulator
  • Good ventilation
  • Highly Dense


  • Non-biodegradable
  • Health hazard
  • High pH levels shifts
  • Relatively expensive

What is Fiberglass?

As the name suggests, Fiberglass is made of thin thread-like glass fibers. The fibers are spun out of glass melted at high temperatures and compressed and sold in form of long rolls or blankets. One might find the story behind the discovery of Fiberglass very interesting. Just like penicillin, this man-made material was pretty much discovered by an accident.

The narrative revolves around a researcher in the 1930’s trying to vacuum seal glass blocks using a high-pressure jet which incidentally spewed out fiber-like threads of the glass. That’s how an accident led to an essential discovery, which eventually became an option for insulating materials. Unlike Rockwool, it is not much of a green product since it uses only 20-30% of recycled material.


  • Low-maintenance
  • Fire-resistance
  • Anti-magnetic
  • Weather-proof
  • Inexpensive


  • Demands gel coating every 5 years
  • Hazard for asthma patients
  • Not water-resistant
  • Poor breathability

Rockwool vs. Fiberglass

1.    R-Value

R-value measures the heat-resistance capabilities of insulating materials. For example, if a material has an R-value of 2, it can mean that a one-inch thick material has a heat resistance rating of 2.

Further, if you buy a 3-inch thick batt do not forget to multiply the R-value with the thickness. Continuing the example, in this case, the R-value will be 6. As a rule of thumb, one should always reach out for the item which has a higher R-value since the higher the R number, the higher is its heat-resistance.

Mineral wool or Rockwool has been assigned an R-value which ranges somewhere between 3.0 to 3.3 per inch. On the other hand, the Fiberglass material has an R-value ranging from 2.2 to 2.7 per inch.

In conclusion, Rockwool is 1.5 times more effective fire-resistant than Fiberglass. Moreover, it has been established that R-value tends to decrease for Fiberglass over time while it does not deteriorate throughout the life of the Rockwool.

2.    Fire resistance and Thermal Regulation

Even though, both the materials have similar responses to fire hazards, Rockwool has better efficiency to counter such life-endangering occasions. The density of insulating material has a direct relation with its fire insulating capacity. The higher the density, the better it is.

Rockwool is relatively denser than Fiberglass making it a preferred alternative. The type of material (basalt rock) used to manufacture Rockwool can melt only at a temperature of 3000° F, allowing it to withstand higher temperatures.

Relatively thinner Fiberglass material can hold fire up to 1100° F only. Anything higher than that and it will start melting. Although Rockwool has better fire sustaining and inhibiting capabilities, it is more susceptible to fire in the first place then compared to Fiberglass.

Coming to thermal regulation, if you reside in areas that tend to become colder in winters then Fiberglass is the best alternative for you since it has better heat retention capacity than Rockwool.

3.    Cost

In case you are running tight on budget then the cost of the materials becomes an important factor for consideration.

A standard R-15 rated Fiberglass insulation for a 4-inch wall will cost around $ 0.50 per square foot. Meanwhile, a Rockwool batt of the same dimension and rating will cost $ 0.62 per square foot. Simple math will suggest that a job of insulating 625 square feet with Fiberglass will cost $312 in contrast to $388 for Rockwool.

In comparison to Fiberglass, Rockwool seems more expensive. At the same time, one might argue that since Rockwool has better performance from all aspects so it’s reasonable that it costs more than Fiberglass. In any case, it’s better to prepare yourself to pay at least $ 0.10 more for Rockwool.

4.    Sound Insulating Properties

As a rule of thumb, the higher the density, the higher will be its sound-deadening properties. Since Rockwool batts are relatively thicker, they showcase a better ability to block sound to and from the room.

One can expect a reduction in transmission of sound waves of up to 4 decibels, meaning that you won’t be able to hear any conversation happening outside the room at a normal level and vice versa. But that doesn’t mean that you can jam all night with your favorite songs playing on a loud music system.

5.    Installations and fittings

Both materials are easy to install, between the studs or on the surface. One can purchase Rockwool in the form of batts, rolls or blankets which can be directly cut and trimmed according to the size and the dimensions of the wall.

Fiberglass is available in both batts and loose fills which make it relatively easy to cover any small areas and do not require a whole blanket. Moreover, even if you don’t have any prior experience you can easily install them in your house.

Just ensure that you wear proper safety gear like a mask, eye-wear, and gloves to avoid any kind of irritation to skin, eyes, or respiratory system. Both materials can be covered with a dense fabric and attached on a wall or a door with hanging strips or glue to function as soundproofing panels.

6. Water Resistance

Apart from fire-resistance, a good insulating material should also be resistant to water. Water retention can assist rotting, corrosion, growth of several microorganisms like bacteria, fungi, and so on.

Fortunately, Rockwool has hydrophobic properties and can keep the water at bay and any problems that can result from water absorption. But if you have decided to go for Fiberglass insulations then you need to remember that it tends to hold the absorbed water which can make it really soggy and sometimes even lead to a significant reduction of insulation effectiveness.

7. Environmental and Health Impact

From the viewpoint of the environment, Rockwool tends to be more hostile in terms that it is not biodegradable, while Fiberglass is very eco-friendly. Even though Fiberglass does not harm the environment as Rockwool, it can still be as hazardous as the latter. Studies have found that if the Fiberglass is not gel-coated regularly then the airborne fiber can create serious problems for asthma patients.

Further, both the materials can cause irritations in the eyes, mouth, lungs, and skin if you come in regular contact. In some cases, it can also slice DNA, cause cell mutations, and inflict long-term ailments like lung cancer.

Because of this it’s vital to place it in a dense fabric that can trap these particles if you decide to use it out in the open, and to wear safety equipment during installation.


1. How long can Fiberglass last? Does it break down over time?

Once installed, Fiberglass insulations can last up to 25 years which makes them the most preferred low-cost and long-term insulating materials. But that doesn’t mean that they don’t deteriorate over time.

2. Which material is better for insulating attics and other closely packed areas?

If the area which requires insulation is difficult to access, like nooks and corners of ceilings or attics, then loose fillings of Fiberglass is the better option here.

3. Is there a need to install a vapor barrier when insulating shower walls with Rockwool?

Rockwool is hydrophobic. It doesn’t hold on to water and moisture hence making it an ideal choice for insulating bathrooms and other moist areas. You can pair it up with other waterproofing techniques.

4. Which material is more rodent-proof?

The Mineral wool or the Fiberglass in itself are not rodent-proof. It has been seen that rats and rodents find it easier to chew through Fiberglass than Rockwool. Using additional rodent proofing methods becomes essential for areas like warehouses or basements.

Similar Posts