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What is Rockwool Insulation?

By Adam Hill
Updated May 17, 2024
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Rockwool insulation refers to a type of insulation that is made from actual rocks and minerals. It also goes by the names of stone wool insulation, mineral wool insulation, or slag wool insulation. A wide range of products can be made from rockwool, due to its excellent ability to block sound and heat. This type of insulation is commonly used in building construction, industrial plants, and in automotive applications.

To make rockwool insulation, minerals and other raw materials are heated to about 2910°F (about 1600°C) in a furnace, through which a current of air or steam is blown. More advanced production techniques are based on rotating the molten rock at high speeds in a spinning wheel, in some ways resembling the way that cotton candy is made. The finished product is a mass of very fine intertwined fibers, bound together with starch. Oil is also added during production to decrease the formation of dust.

The individual fibers of rockwool insulation are good conductors of heat on their own, but rolls and sheets of this insulation are highly efficient at blocking heat transfer. They are often used to prevent the spread of fire in buildings, in light of their extremely high melting point. As with other types of insulation, rockwool can play a large role in reducing energy consumption in homes and businesses. Made of natural materials, rockwool insulation is safe to manufacture and use, when proper guidelines are followed. Decades of research have shown that it poses little to no health risk to humans, including that of respiratory and other cancers.

While it is not attractive to rodents, rockwool can pose problems in other ways, especially if allowed to become wet. Rockwool insulation is able to retain a large amount of water, although gravity will make it slowly drain out, as long as it has a way to escape. This ability to hold water, coupled with the fact that it retains a certain amount of air at all times, has made rockwool a popular growing medium in horticulture and hydroponics. These properties of rockwool allow for good root growth and nutrient uptake. It also provides a good mechanical structure for the plant, keeping it strong and stable.

In its natural state, rockwool has a relatively high pH, which is unsupportive of plant growth. In order for it to be suitable as a medium for growing plants, it must be treated to lower the pH to a more stable and neutral value that will allow the plant to thrive. This treatment involves soaking the rockwool in pH-adjusted water for at least 24 hours before use.

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Discussion Comments
By anon960638 — On Jul 11, 2014

Is rock wool pulverized when used as ceiling or wall heat and sound insulation?

By anon954466 — On Jun 02, 2014

What is the difference between rock wool and glass wool?

By anon316752 — On Jan 30, 2013

What is the cost savings each year and which one is better?

By anon278047 — On Jul 03, 2012

@anon36310: That stinks! So sorry!

By anon161611 — On Mar 20, 2011

Is Rockwool insulation the best one for sound between bedrooms and such?

By anon161108 — On Mar 18, 2011

what is the difference between rockwool and mineral wool?

By anon131856 — On Dec 04, 2010

Rock wool insulation was used for what seems like forever as a construction insulation. It's just as good as glass spun (fiberglass) but has none of the skin irritation. It also doesn't emit a smell in high humidity and temperature as does spun glass.

Don't get me wrong --it's murder on the lungs and eyes. And anon36310 is correct. Once it's there, it's there until you "wipe" it off as he said. I'd say scrub, hard.

I had blown over the top of mine with fiberglass and now have an r 50 that's nice and toastt. In conclusion, rockwools is fine but there is always going to be some improvement in material and installation practices.

Hope this was helpful and anon36310, I'm hacking whenever I breathe it in also.

By rolling68 — On Jul 13, 2010

Rockwool insulation is an attractive choice because it does not present skin irritation the way that fiberglass does. Also, unlike fiberglass insulation, the rockwool variety does not emit a pungent odor in high humidity and contains 75 percent post-industrial recycled content.

By CrepeTime — On Jul 13, 2010

Rockwool insulation accounts for approximately 20 percent of the mineral wool industry.

By anon36310 — On Jul 11, 2009

Used properly, Rockwool Insulation is not harmful. I bought a 10yr. old house 5 years ago; and started having allergy and sinus, eye infections, skin rash, etc. a few months later. A big mystery. After 4 years, I realized there was "something wrong" with my furnace, causing it to blow dust that caused me coughing spells and all these infections.

The problem was finally located: A lazy installer had dragged the expansion pipe for the return air duct through the attic to connect the other end, and scooped up about a bucket of rock wool into the pipe. It had no way out, and had been spinning around for 14 1/2 years, causing the dust! I have had professionals replace that return air pipe, clean all the floor vents, clean windows and window coverings and carpets. Over $1200 so far, and now learn that the floor vent system under the house has to be replaced, because this stuff sticks to the sides of the vents and anything else it comes into contact with! I blows the stuff into the house when I turn on the furnace. It does not blow away, it has to be *wiped* off!! I wish I could shake the dummy who did this!!

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