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Rockwool Insulation

Awesome for 3 Reasons

As Seen On
by Jeff Patterson in DIY Bathroom Remodel
Rockwool Insulation Feature

Rockwool insulation is awesome.

There’s no contest.

A few years back my wife and I remodeled our master bathroom.

We researched different insulations and concluded Roxul (at the time) was the best option.

Roxul recently changed it’s name to Rockwool.

So we partnered with them to get the word out because we believe in Rockwool.

Plus we have three cool demonstrations that show why you should use this insulation in your home!

What is Rockwool Insulation Made Of?

I’ve been asked this question a lot by readers and friends:

What the heck is Rockwool insulation? 

Rockwool insulation is a rock-based mineral fiber insulation made from Basalt rock and recycled slag.

Basalt is a volcanic rock that’s naturally made by the Earth. Think Hawaiian islands.

Slag is a by-product of the steel and copper industry. Think Pittsburgh Steelers.

We’re from the Burgh – couldn’t resist a Steelers reference.

Rockwool is made when Basalt and slag are melted then spun into fibers. Those fibers are then made into batts which slide between studs or joists.

Add Roxul around windows

In case you’re wondering, between 16% to 40% of Rockwool is made from pre-consumer recycled material.

Let’s get into the 3 reasons my wife and I chose this type of insulation.


What is the Best Insulation for Soundproofing?

Research Google and you’ll find Rockwool insulation typically gets voted one of the best options for soundproofing.

It helps with both low and high frequency sounds.

Quick story, back in college my first dorm was just below a helicopter pad near the local hospital. Between that and ambulances it was a rough first semester.

Bottom line:

If you want better sleep and live in a noisy area then Rockwool could help.

Sure, you’ll have to remove the existing drywall or plaster. But installing Rockwool is easy and quick.

And it can be cut with either a utility, drywall, or bread knife…clean that bread knife after using it.

Cutting Roxul is easy

Reason #1 is soundproofing.

We do a lot of bathroom remodeling tutorials and constantly think about which products work best in wet conditions.

Which brings us to the following…

What Happens When Rockwool Gets Wet?

It repels water and doesn’t lose R-Value.

This is truly important in bathrooms because a certain amount of water vapor gets into the walls while you’re showering.

We learned this a long time ago while attending a Schluter class on KERDI-BOARD.

As long as the rate of water vapor infiltration is lower than the rate of evaporation the stud wall should be okay.

Fiberglass insulation on the other hand will lose R-Value over time if exposed to water vapor.

Rockwool insulation is moisture resistant yet vapor permeable. If it becomes damp or wet, the insulation (when dried out) will maintain the original performance characteristics.

Furthermore, stone wool insulation does’t wick water.  Any water that contacts the outer surface will drain and not be absorbed into the body of the insulation.

Reason #2: Rockwool is water resistant!

Rockwool Insulation repelling water

Here’s the deal:

Rockwool also isn’t a food source for mold since it’s inorganic.

And that’s a HUGE deal for bathrooms.

Finally, Reason #3…


Rockwool is Fire Resistant

Anyone with children hates the idea of a house fire.

This scares the heck out of me because my wife and daughters are the most important people in my life.

If something can delay the spread of fire then I’ll use it.

Rockwool is fire resistant up to 2150 Fahrenheit.

As such, it will give my family time to escape from a fire.

Reason #3: Rockwool is fire resistant!!

In today’s video Steve has his hand on a piece of Rockwool and there’s a flame on the other side. This demonstrates how Rockwool can protect you from fires.


What’s Next

Our tutorial on how to insulate walls with Rockwool is great if you need guidance.

Youll see that I mention Roxul a lot in that tutorial, but Roxul is exactly the same as Rockwool.

And by the way, if you’re remodeling a shower and use Rockwool with KERDI-BOARD or  Wedi’s shower system there’s no need for a vapor barrier.

This is primarily due to the KERDI-BOARD or wedi.

Grab our free guide if you’re doing a DIY bathroom remodel – it shares how to remodel a bathroom in 10 days or less

Get Our Guide


Thanks as always for reading, watching, and being part of our awesome community.

Ask your questions below and we’d be happy to help.


Jeff Patterson





  1. Dale says:

    Can Rockwool be used to insulate attics? Thank you.

    1. Great question Dale, yes. You can also stack batts to achieve higher R-Values.

  2. Greg Keferl says:

    What’s the cost of Rockwool compared to standard paper faced insulation?

    1. Good question Greg, Rockwool costs about $47 for roughly 59 square feet. The cost for paper-faced insulation will depend on the brand you choose and the R-Value required. I don’t mind spending $47 on the stone wool as it should last a long time. And it won’t degrade if it gets wet or moist.

  3. mineralwool says:

    This post was very useful. Can I use it?

  4. Mineralwool says:

    Exellent Information , Write More a Bout This For Us.

  5. Paul Papamarkos says:

    Do I have to use a vapor barrier needed after install?

    1. Depends on your backer board, if using a foam backer board like Kerdi-Board or Wedi then no.

  6. Kim says:

    How do you feel about the manufacturing process of rockwool? I understand it puts out a lot of pollution such as VOCs, NOx, PM 2.5, PM10 among other things and can be quite terrible for the areas around the plant. Is it really a great, green product if the company pollutes the communities where it is made? I want high quality insulation in my home but have a hard time with a company that is essentially greenwashing their product.

  7. Matt says:

    I’m converting a one cargarage to a room. I will be raising the floor about a foot. I will frame it out and it won’t touch the concrete floor. I will insulate it with Roxul.
    Since it’s not going to make contact with the concrete, do I need a vapor barrier? Thanks

  8. Dan says:

    Would you still recommend it for a first floor big room (kitchen and family room) with a bedroom above it? Seems like the choice is better blown in cellulose (less drywall removal) vs roxul (a lot of drywall removal). This is strictly for sound abatement between floors.

  9. Michael McDonagh says:

    Can you use Rockwool on a flat roof?

  10. Cathy says:

    I would like to do a crawlspace encapsulation. I have as uneven rock wall foundation and do not want to use spray-on products. Can rock wool be used on the stone walls? Should the floor vapor barrier be run up the walls behind the rock wool?

  11. Jeannine says:

    Can Rockwool be blown in? We have a contractor that says he grinds up Rockwool material, then blows it in.
    Is that something that can be done?


  12. Kathy Nowotny says:

    Question…We have an 1860 2story Victorian home with slate roof, balloon construction. Need better insulation! Very drafty. Would Rockwool work under the slate? Or better in attic floor, although side walls and stairwell are acting as chimney, so we’ve been advised to insulate the roof.


  13. George says:

    I came upon a project where a prior contractor had built perimeter walls in a basement, no vapor barrier, no insulation, wood studs, sheet rock on the interior.and baseboard heat. With the studs so close to the foundation it would be difficult to install an effective vapor barrier. Could Rockwool be installed without consequence? The basement is relatively dry, the walls open at the top for breathing.

  14. Steve James says:

    Can rockwool be used to soundproof a return air filter for a dust collector? Air is returned to our building but at about 90 decibels. We need to soundproof it, but the air still needs to flow through back into the room. Will rock wool work?

  15. Leslie Bishop says:

    Do i need airflow in a flat ceiling.I live on the ground Floor
    And because of electrics

  16. House Insulation Auckland says:

    It’s a great source of knowledge; I think it will be helpful for lot of people who are looking for learning more about the Rock wool insulation. Thanks for this wonderful content and for sharing this article with all of us around the world. If you are looking same kind of valuable information, then can also visit

  17. Eggca says:

    Can i use Rockwool around plumbing pipes in the outside wall of my house? Thank you.

  18. Tish says:

    There is some free Rockwool Sound proofing insulation that I’m interested in picking up to line the finished walls under the stairs to use as a sound studio. Can I use this material and how to best install? The floor is ceramic, so I’d buy a throw rug on top. Studio will have a chair and existing file cabinet as a desk.

  19. LYNN W HUGHSON says:

    Roxul was made better. didn’t fall apart easily like rockwool does, was more water resistant, this stuff soaks up water like pink fiberglass and
    doesn;t bounce back the same as roxul did. they do not make it the same unless i got a bad batch.

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