Rockwool Insulation Review: Specifications, Cost, and Other FAQ

Whether you’re looking to soundproof your walls, insulate some wires and pipes, or make acoustic panels, Rockwool insulation is probably the first product you’re going to consider. But is it really as good as people think it is? More importantly, is it worth the price tag? You’ll find out in this comprehensive review of Rockwool insulation.

If you’ve ever worked with Rockwool batt or blanket insulation, you may have noticed how easy it is to work with. It fits perfectly between the standard width wall studs or ceiling joists and stays exactly where you put it.

On top of that, Rockwool insulation can supposedly hold its own even against open flames and running water. But before we can unpack those claims, let’s answer the most basic question of all.

What Is Rockwool Insulation Made Of?

Though many people use the word “Rockwool” to refer to any kind of mineral wool insulation, Rockwool (previously known as Roxul) is a brand name. Still, the kind of insulation this company makes is pretty much explained in its name. It’s true. The soft batts many people already have in their walls are literally made of stone.

To be specific, the final product is a combination of volcanic rock (basalt) and slag — a by-product of the steel and copper industry. Between these two ingredients, you can already see that this kind of insulation is a fairly sustainable construction material. After all, both basalt and slag are abundant.

How Do the Solid Materials Become Fibers?

So how do these solid substances become the soft yet sturdy product we all know? Well, the process begins when they enter an oven along with a healthy helping of coke. And no, we’re not talking about the kind you drink here, but the kind that’s made from coal. So that may be a negative point on the sustainability side of things.

In any case, once these ingredients melt, the inside of the oven spins, creating a frothy mixture. But the process of making rock wool doesn’t end there. To create blanket or batt insulation, the manufacturer still needs to fuse layers of this material. To do that, the cotton candy-like fibers are put in a machine that deposits layers of it on top of each other in zigzag motions.

Between those layers, the company adds thin layers of oil and a proprietary binding solution. From that point, the stone wool blanket goes through rollers that compress it to achieve a certain density of insulation. Finally, the product goes through an oven once again, where the binder is cured. Once the insulation is rigid, it’s ready for cutting and packaging.

Is Rockwool Insulation Safe?

Now, before we get into the basic features of this product, you may be wondering whether this kind of insulation is safe. As you’ll find out later on, certain kinds of insulation can be tricky to work with. Some require full safety gear, as loose particles can get into the lungs and irritate the eyes and skin. But is that something you need to worry about with Rockwool?

Well, as we have established, most of the materials that go into the oven to create mineral wool are harmless enough. Even though slag is a byproduct of the steel industry, it doesn’t contain any dangerous heavy metals. Yet, depending on the manufacturer, the production of mineral wool insulation can include some potentially hazardous binders.

In the past, Rockwool has used formaldehyde to bind mineral wool fibers. As you can imagine, that could be a problem for anyone installing the insulation. After all, the batts might release these compounds during the process. Worse still, some experts have claimed that this issue can also impact the air quality inside the home later on.

Luckily, Rockwool has already addressed this issue. On the one hand, the manufacturer admits to still using the same binder during the production process. Yet, the company claims that the high temperatures that cure the binder essentially neutralize its effects. Moreover, the company notes that its SAFE’n’SOUND, ComfortBatt, and AFB lines have all received the GREENGUARD GOLD status, guaranteeing superior air quality inside your home.

Of course, if you’d rather avoid dangerous chemicals altogether, check out Rockwool’s AFB Evo line. Even though that insulation contains alternative binders, its performance should be on par with the standard Rockwool products. But what does that even mean?

The Basic Properties of Rockwool Insulation

Now that you know what mineral wool is, you probably want to know what makes it such a popular construction material. Well, if you just want to know the bare necessities, you’ll find them printed on the packaging.

Mineral wool insulation is generally firm, allowing it to stay between wall or ceiling joists without any fasteners. The tightly packed stone wool provides a friction fit and stays in place without sagging for years or even decades.

On top of that, there are several other advantages to insulating your home with stone wool. For one, the material provides ample protection against fire, moisture, and even pests. Additionally, thanks to the high density of the product, it has excellent sound dampening properties.

With all that in mind, let’s take a closer look at some of the key features you should keep in mind when shopping for batt or blanket insulation.

R-Value

When construction professionals compare different insulating products, they usually start with the R-value per inch. That property tells us how well the fibers insulate against air loss and resist heat flow. So as you can imagine, the higher that number is, the better.

As we have previously established, the R-value of your insulation is particularly important if you’re looking to prevent heat from leaving through your walls. Basically, you wouldn’t want to use insulation with a low R-value in the basement, attic, and external walls. If you must skimp somewhere, let it be on the interior walls.

After all, you probably won’t be as concerned about losing air to other rooms within your household. Then again, if you can afford to use insulation with a high R-value all over your home, that would be the best solution.

According to experts, it’s generally a good idea to use insulation with an R-value between 13 and 25 for external walls. But does Rockwool have anything in that range? Well, the company did recently expand one of its product lines to include insulation with an R-value of up to 38. Needless to say, that’s about as impressive as it gets.

Still, according to the company, consumers shouldn’t fixate on the R-value alone. Fire resistance, sound control, and the rigidity and flexibility of the insulation are just as important. With that in mind, let’s talk about some of the other features that can tell you how well a product will perform in those departments.

Density

When it comes to insulating your walls, density is the name of the game. The denser your insulation is, the more air it will be able to trap, thereby stopping the transfer of heat and sound. Dense insulation should ensure that your home remains hot in the winter, cold in the summer, and quiet, year-round.

According to most experts, mineral wool products tend to have the highest density out of all the types of insulation. Even so, Rockwool makes products with different levels of mass. On one end of the spectrum, you have the basic Rockwool Roll with a density of 22 kilograms per cubic meter or 1.37 pounds per cubic foot of material. In comparison, the most compressed products in the company’s lineup can have a density of over 1000 kilograms per cubic meter (62.4 pounds per cubic foot).

As you can imagine, many of the products in Rockwool’s lineup fall somewhere between those extremes. Chances are, the insulation you’ll be looking at will have a density of 40–140 kilograms per cubic meter of material. And naturally, this feature of the insulation will also determine the NRC — or noise reduction coefficient — rating it boasts.

Thickness and Other Dimensions

As with the previous category we discussed, Rockwool also makes products that fit cavities of different depths. Comfortboard, the thinnest product the company makes, is only about an inch and a half thick. Yet the standard thickness of most mineral wool insulation batts is closer to two or three inches.

The company’s ComfortBatt line comes in sizes that fit steel studs and wooden ones. As you can imagine, the products that are made to fit into steel frames are thinner, ranging between 2.5 and 6 inches thick. On the other hand, batt insulation for wooden studs can be 3.5, 5.5, 7.25, and 8 inches thick.

Since mineral wool can be compressed to a ninth of its size, the product will still be easy to ship, too. Thanks to the relative rigidity of mineral wool, the compression won’t even reduce the R-value of the product. Unlike some other types of insulation materials (such as fiberglass), mineral wool doesn’t require fluffing upon delivery. Once you take it out of the packaging, it’ll bounce back to its original shape without much prodding.

So what about the other dimensions of batt insulation, namely the width and length of the panels? Well, most manufacturers aim to make the width of the panel correspond to the space between the standard wall joist. Because of that, most Rockwool products are either 16 or 24 inches wide, and 48 inches long.

Price

At this point, you pretty much know everything that might convince you to opt for Rockwool insulation. There’s just one thing that might still prevent you from taking the plunge — the cost of mineral wool insulation. So what kind of price tag are we talking about?

As always, the total cost of insulation will depend on several factors, such as the size and R-value of the product. All those specs will drastically impact the price point. For example, getting enough R15 insulation to cover a square foot of space would cost about $0.62. Conversely, the same amount of R22 insulation would be twice as expensive, if not more.

Generally speaking, mineral wool insulation is twice as expensive as fiberglass. On the other hand, it’s less expensive than natural alternatives like sheep’s wool insulation. So it’s all a matter of perspective. Besides, Rockwool’s product is superior to most other kinds of insulation, so we should be willing to put up with a steeper price point.

How Does Rockwool Compare to Other Kinds of Insulation?

Now that you know the benefits of using Rockwool, let’s spare a moment for the competition. Here’s how Rockwool compares to fiberglass and spray foam insulation.

Rockwool Insulation vs. Fiberglass

When it comes to competition, Rockwool really only has one rival — Owens Corning. The company is primarily known for manufacturing pink fiberglass insulation. Take a wild guess as to what it’s made of!

Owens Corning R-13 Faced Insulation Roll
  • Individual Roll - 15 Inches Wide x 32 Feet...
  • Ideal for use in 2x4 walls; providing...
  • With less dust than other fiberglass...
  • Compression packaging from Owens Corning...

All jokes aside, the process of getting glass into a cotton candy consistency is similar to the one used to produce mineral wool. In this case, the ingredients that go into the furnace are sand and recycled glass. Soda ash is added to conserve energy by reducing the melting point of sand. Lastly, the manufacturer also throws limestone into the mix to prevent the glass from dissolving in water.

After it melts, the glass goes into spinning bowls, where compressed air is used to cool it and shoot it out of tiny holes. That effectively turns the glass into fibers. The resulting material is stacked on top of each other with pink glue between each layer.

At that point, some fiberglass insulation receives a craft paper or vapor foil facing on one side of the material. Then, the manufacturer can either cut it into batts or roll it up. Owens Corning even offers loose-fill fiberglass insulation. Yet either way, the resulting product is inferior to mineral wool by any measure:

  • It’s not fire, moisture, or pest-resistant
  • It’s three times lighter and less dense than stone wool
  • Unlike Rockwool insulation, it can’t bounce back after compression
  • Because of that, it tends to lose R-value rapidly even once it’s in the wall
  • Since it can’t provide a friction fit, you’ll need to staple it to the wall studs

In fact, the only thing fiberglass insulation has going for it is its lower price point. But that’s not enough to recommend it when the experience of using it is otherwise so lackluster.

Rockwool Insulation vs. Spray Foam

Comparing Rockwool insulation to spray foam is much more difficult than comparing it to fiberglass. After all, these two are completely different kinds of products. Still, we can try to compare the way spray foam performs relative to mineral wool insulation.

First things first, you might say that spray foam provides a more complete seal. Even though mineral wool can provide a friction fit, expanding foam might fill that space much more snugly. Moreover, it will get around any oddly shaped areas around pipes and into the cracks in the wall.

That should prevent any noise and hot (or cold — depending on the season) air from escaping your home. Yet the efficacy of the solution will ultimately depend on the thickness of the application and the type of foam you’re using, among other factors.

Now, applying the foam should be a fun task, though it may require additional equipment. Say what you will about batt insulation, but at least installing it doesn’t take a foam gun. But what does the process of installing Rockwool insulation look like, anyway?

How to Install Rockwool Insulation

Before you can start testing out your friction fit mineral wool insulation, you’ll want to get your hands on a few essentials. You’ll need:

As we have established, the modern mineral wool insulation isn’t as dangerous as previous iterations of the product might have been. Still, the safety gear should protect you from any potentially harmful particles that might come up as you start cutting the batts.

Push the Insulation Into the Wooden Frame

If you’re looking to get Rockwool insulation, chances are, you either need it for your walls or to create acoustic panels. Luckily, the installation process should be easy enough no matter which option you’re going for.

Once you have a wooden frame that’s ideally either 16 or 24 inches wide, you’ll simply push the insulation panel in. If you’re working on vertical wall studs, you should start at the top. Or if you’re making sound-absorbing panels, just make the frame according to the batt dimensions. As we have established, the insulation should stay in on its own, no stapling required.

If your walls are shorter or taller than 8 feet, two 48-inch long batts per cavity won’t get the job done. Luckily, cutting mineral wool is surprisingly straightforward.

How to Cut Rockwool Insulation

Remember that serrated knife you got at the beginning of this project? Well, here’s your chance to use it. The relatively rigid structure of mineral wool makes this kind of insulation fairly easy to cut through.

So adjusting the length of the panels and tweaking them to fit around electrical boxes and pipes should be a piece of cake. First, put a panel against your cavity and mark out where you need to cut with your knife. Then, move the batt to the floor and saw through the material until it fits perfectly into the wall cavity. It really is as simple as that.

Do You Need a Vapor Barrier With Rockwool Insulation?

Once you have stuffed all your wall cavities, you might find yourself wondering whether you need a vapor barrier. Well, considering the fact that mineral wool is highly resistant to moisture, it may not be necessary. Remember, volcanic rock is naturally hydrophobic. Between that and the oils that coat the mineral wool during the production process, Rockwool insulation doesn’t need a vapor barrier.

Still, if it would give you peace of mind, you could install one. Some areas of your home, such as bathrooms and kitchens, could probably use some extra protection. Ultimately, the decision of whether you should use a vapor barrier over your Rockwool insulation or not is completely up to you.

Does Rockwool Live Up to Expectations?

If you went into a home improvement store and asked for the best insulation batts money could buy, chances are, the sales associate would hand you one of Rockwool’s products. But can we justify the blind faith people have in this company?

After all, the company’s main product, mineral wool, hits every check mark that makes batt insulation great. For one, it’ll effectively absorb any noise that tries to make its way in or out of your home. Additionally, the stuff is fire, moisture, and pest-resistant. Already, that’s more than you could say for most other kinds of insulation.

While we’re singing Rockwool’s praises, it’s worth mentioning that the production process is about as sustainable as it can get. Even the main concern people had about using Rockwool insulation — the use of formaldehyde as a binder — has been dispelled. So if you can spare the cash, Rockwool is the way to go.

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