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Model #RXCB351525

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R-15 Comfortbatt 3-1/2 in. x 15 in. x 47 in. Fire Resistant Stone Wool Insulation Batt (59.7 sqft)

Buy 15 or more $38.22 /roll
  • Easy to install with a friction fit and a consistent R-Value
  • Compression pack, one bag includes 12 pieces and covers 59.7 sqft
  • Sound reduction and fire resistance designed for exterior walls
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Product Overview

ROCKWOOL Comfortbatt is a semi-rigid stone wool thermal batt insulation for exterior wood and steel stud applications. It features a unique flexible edge that allows for easy installation and helps prevent over compression to maintain its R-value. Non-combustible and fire resistant, Comfortbatt will not develop toxic smoke or promote flame spread, even when exposed directly to a fire. It also offers water and moisture resistance and excellent sound absorbency. Comfortbatt is an effective way to improve a home's energy efficiency. It is GREENGUARD Gold Certified and contributes to a healthier indoor environment.
  • Excellent thermal performance providing a high R-value per inch
  • Non-combustible and fire resistant, stone wool works to contain a fire and prevent its spread.
  • 3-1/2 in x 15-1/4 in. batt sizing is designed for 2x4 wood framed construction spaced 16 in. on center
  • Comfortbatt applications include: exterior walls between studs, basement walls, crawlspaces, attics and cathedral ceilings and exposed floors
  • Stone wool provides excellent noise reduction and sound absorption to help you create quieter, more productive environments.
  • Water resistant, stone wool does not rot or promote the growth of mildew, fungi or mold
  • Lightweight and easy to install, cut using a serrated knife and compression fit into place
  • Friction fit batts conform to normal variations in stud centers caused by distortion or warping
  • Greenguard gold certified for indoor air quality
  • Click here to learn more about Eco Options and Energy Efficiency
  • Installation Breakdown:

    basement wall R-15 installation breakdown

  • Buying guide and insulation calculator:

    insulation buying guide
    Insulation calculator button

Additional Resources

From the Manufacturer

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Cover Area Per Bag (sq. ft.)
59.7 ft²
Coverage Area (sq. ft.)
59.7 ft²
Product Length (ft.)
4 ft
Product Thickness (in.)
3.5 in
Product Width (in.)
15.25 in


Bag Size
4 ft. x 16 in. x 24 in.
Batt/Roll Size
4 ft. x 3.5 in. x 15.25 in.
Compatible Install Surface
Faced or Unfaced
Insulation Features
Friction Fit
Insulation Location
2x4 Wall,Attic,Basement,Ceiling Insulation,Crawlspace,Floor
Insulation R-Value
Insulation Type
Number of Pieces
Pack Size
Product Weight (lb.)
49.7 lb
Roll or Batt

Warranty / Certifications

Warranty Information

Questions & Answers

Typical questions asked about products:

  • Is the product durable?
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Customer Reviews

  • 4.9
    out of 588 reviews
  • 99%recommend this product
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Showing 1-10 of 588 reviews
The best product!
I have replaced all of the old 1955 insulation in my home and i am working on the last room right now.I'm using R14 for 2 x 4 application inside my walls.I am so glad that i'm using Roxul as it has already shown to lower my heating bills and the accoustics changed right away.I don't hear much noise outside anymore.It is so easy to install and it's not itchy,i'm cutting the pieces with a bread knife.Thanks guys for a great product!
    • Recommended
    This should make regular fiberglass insulation obsolete
    I'm remodeling my 1950 mid century modern home one room at a time. I started with the hardest room to heat & cool, knocked out the old plaster & had the room sprayed with rigid & soft foam. The guys rushed the job & left some thin spots and even bare wood showing thru. I wanted to fill voids with Roxul but could not find it anywhere in Oklahoma so I hung the drywall anyway. Since then I've found a dealer 30 miles from me that can order it. I've since used Roxul in my sun room & garage. I like it better than the foam & I can easily install it myself.
      • Recommended
      I used this to replace old fiberglass batts in my upstairs. It is very nice to work with, and fil...
      I used this to replace old fiberglass batts in my upstairs. It is very nice to work with, and fills the wall cavities completely without gaps, unlike the fiberglass batts that were there. It really shines around electrical outlets and obstructions that you would typically have a very hard time filling well with anything but dense pack. I used the mineral wool insulation knife, but you can just as well use a long bread knife or even an electric meat carving knife. Any serrated blade. I had odd stud spacing and was able to use whole batts combined with vertically 'ripped' batts to fit the cavities. A straight edge is handy. Wear a dust mask.
      • Verified Purchase
      • Recommended
      Better Conformance to Joist Spacing
      Fiberglass batts depend on springback to original shape, from large compression in packaging. That springiness then results in buckling if a bit oversize for the space. Rockwool doesn't do this. Lost contact with confining surfaces destroys insulation value.
        130 year old church restoration, ideal product
        Installing comfort batt insulation in the walls and floor of a 130 year old William Critchlow Harris church/cottage upgrade. As this structure is a 'balloon' design, fire concern was paramount. Simple installation even with so many cuts, and huge long term benefits. Ideal application for your product.
          • Recommended
          I am happy with this product.
          I like it when i get asked what i'm putting into my walls.I let friends know that this product is safe to handle and not itchy.I'm using a bread knife to cut pieces to fit.I've got peace of mind knowing it's not going to grow mold,it's fire resistant,easy to install and i won't hear as much outside noise in my home.Right now i am installing this product and i am 3/4 completed.
            • Recommended
            We won't use anything but this product in our builds!
            We do both custom and high volume manufacturing for tiny homes on wheels. It's important to us that the products we spec out to use are easy to install and work effectively for our applications. This product does exactly that. Sounds carry far and wide even in tiny homes. So, when we have new families moving into a small space, this product makes an excellent noise dampener in between closed off rooms to provide an element of privacy where it can normally be hard to find. Nevermind its obvious positives, this product is just far superior at the end of the day. It's our gold standard for each home that we send out of our shop and it makes us proud!
              • Recommended
              Ive been a fan of Roxul aka "Rockwool" ever since Mike Holmes Introduced it to his show Holmes on Homes. Had to wait a couple of years before it came to the States but when it did, i was elated!!! I got to try the water test and burning it, and boy was it amazing, just as described and show. I will never ever use the pink insulation ever again!! Re-insulating that garage picture i sent you in 90degree heat, after done that garage kept a temp of 70 degrees, i was extremely impressed!! ROXUL HEAD 4 LIFE!!!!!!!
                • Recommended
                I've used Roxul ComfortBatt throughout my entire house for all...
                I've used Roxul ComfortBatt throughout my entire house for all the exterior facing walls. They make a huge difference in terms of thermal insulation and vapor barrier (just remember to also use the 3 mil+ poly over). The product is very cost effective when you're on a tight budget.
                • Verified Purchase
                Remodel - exterior wall on interior of family room - I like the properties of this product for it...
                Remodel - exterior wall on interior of family room - I like the properties of this product for its density (some sound acoustical value) and that it is mineral rock wool packed into 4 foot batts. NOTE: these batts have NO vapor barrier. where vapor barrier is needed (typically exterior/garage walls), I added a barrier film to the interior side of the wall where remodeling by using Certainteed "Membrain" vapor management film (remember, "paper to the people side of the wall!"). The Roxul product is easy to install in the wall cavity and with a serrated insulation knife very easy to cut in around boxes and blocking. It provides a solid fill in the wall void and has very little "dust or raveling. the batts are slightly wider that the standard stud spacing making it easy to simple push them into the void without stapling or fastening (and has a full contact seal). Be sure to match the spacing of studs or joists to the width of the batts (typically studs or joists are 16" or 24" spacing) and to the depth of the space (3 1/2 inch or 6 inch.. depending on studs or joist size. When encountering a wire crossing the stud cavity I simply cut the batt parallel to the wire , pushed the batt under and over the wire (make sure it goes behind the wire in the wall void). provides a complete "air pocket-free" seal. Also, these batts are rated at R-15 for 2x4 stud cavity providing more insulating value (fiberglass batts are typically R-13 for 2x4 cavity). it is thought that rock wool also discourages rodents but I have no proven evidence that it does and have seen where they chewed through some old rockwool batts (non Roxul products) on other projects. Today's products may have been treated to deter rodents but it is not advertised as such to my knowledge. easy to use, quick to install, clean wall finish when done.
                • Verified Purchase
                • Recommended
                Showing 1-10 of 588 reviews