Mineral wool with cellulose inclusions from a 2002 home  (C) Daniel FriedmanComposition of Mineral Wool Building Insulation
Ingredients in "rock wool" stone or vitreous fibers

  • MINERAL WOOL / "Rock Wool" COMPOSITION - CONTENTS: what are the ingredients or components of mineral wool, slag wool also commonly referred to as rock wool used for building insulation. Photographs of mineral wool including in-situ and photographs of Gold Bond Rock Wool insulation under the microscope.
  • POST a QUESTION or READ FAQs about Rock Wool mineral fiber insulation & microscopic examination or identification of mineral wool fibers

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Rock wool or mineral wool insulation composition:

This article describes the composition of mineral wool or slag wool insulation used in buildings. We include images of Gold Bond rock wool and other newer mineral wool products both in place in buildings and at higher magnification under the microscope. Details given here also help identify and confirm mineral wool or slag wool in the laboratory as well as in the field.

This mineral wool or "rock wool" insulation article series illustrates and describes mineral wool or "rock wool" and slag wool insulation materials. Rock wool or "rockwool" insulation is also called mineral wool and slag wool though there can be differences among the components of these insulations. We describe old-house or "antique" mineral wool insulation as well as modern mineral wool insulating products still used in buildings.

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What are the Constituents of Rock Wool or Mineral Wool Insulation? (it's not asbestos)

Mineral wool with cellulose inclusions from a 2002 home  (C) Daniel FriedmanOur photograph at page top shows modern mineral wool insulation sampled in a home constructed in 2002. This mostly-white mineral fiber insulation includes cellulose (chopped paper including newsprint) fragments that you can see as red and blue particles.

These paper fragments and fibers are a minor constituent in mineral wool insulation, possibly added to reduce settlement or in some building samples these particles might be volunteer fragments from nearby cellulose insulation.

Just to add to the confusion about what to call this insulation, the insulation industry calls a range of products "mineral wool" and includes under that name: fiberglass (a very different material), slag wool, rock wool, "rockwool", stone wool, and vitreous fiber. And as we explain below, though that term has been widely used generically in scholarly research, ROCKWOOL®, a Danish stone wool insulation company has trademarked the term "rockwool".

Rock wool or slag wool is a naturally-occurring mineral fiber that looks like chopped white cottony material. (It may have originally been formed by wind blowing across streams of lava from erupting volcanoes.)

As we noted at our home page for this product, MINERAL WOOL - ROCK WOOL INSULATION

Mineral wool is produced by melting rock and slag using coke as a fuel. The molten minerals are spun into fine fibers using high-velocity spinning rotor and a stream or air or steam.

A binder is applied to the fibers that are then collected on a wire mesh conveyer. The mineral wool fibers are then cut or granulated and packaged for shipment or they are further cured with additional binder so that the resulting fiber blanket can be cut into insulating batts and in some products, combined with a vapor barrier or facing.

Mineral wool insulation l is currently produced in the U.S. in Indiana, North Carolina, Texas, and Washington State as well as being produced in other countries. We list some current producers of rock wool or mineral wool insulation at Reviewers, below.

In an attic rockwool is typically about 1 1/2 pounds per cubic foot in density. In building walls this material is installed in more dense sprays of four to five pounds of material per cubic foot.

At roughly 1.2 pounds per cubic foot, rockwool or mineral wool has an R-value of R-30 (heavier than fiberglass).

Rock wool as a building insulating material remains in active use in the U.S. and has been reported in application in the Southern U.S. in the mid 1980's and continuing at least into the mid 1990's. [Home Energy Magazine Online, July/August 1997].

Currently stone wool, to use a synonym, is also used in acoustic control coatings for noise control, marine applications, fire-resistant coatings or insulations, and in vibration control systems. In addition, a number of researchers have studied the horticultural use of "rockwool" citing its advantages in the control of certain pathogens that affect crop growth. This research is cited in detail at REFERENCES.

Modern mineral wool, widely referred to as "rock wool", is a manufactured product comprised of a mix of limestone, slag waste from steel blast furnaces, and basalt or diabase. Typically but varying by manufacturer, mineral wool insulation is about 3/4 steel slag and 25% basalt rock. Some rockwool producers use nearly pure recycled steel slag.

Similar to the production of fiberglass, rock wool is manufactured by heating these materials and spinning them into fine fibers that are then often applied in a sprayed-on chopped fiber form. Unless product packaging (or on older mineral wool installations, labeled vapor barriers) is present it is almost impossible for a consumer to identify the original brand or source of stone wool or mineral wool fiber insulation that has been installed in their home.

Watch out: about mixing trademarked words in normal human speech. Within this article and at this article's REFERENCES section more than 50 scholarly citations as well as many reader inquiries make generic use of these terms: rockwool, rock wool, stone wool, mineral wool, and slag wool and vitreous fiber.

However Rockwool® is a registered trademark of Rockwool International. In this un-dated ROCKWOOL® letter received on 11 November 2016 the company has asked that their term "ROCKWOOL" be used only to describe their own products and that the terms "mineral wool" or "stone wool" be used for other products not marketed by ROCKWOOL International.

ROCKWOOL® is a registered trademark of ROCKWOOL International A/S and should be distinguished by our readers from all of the more-generic names or other product names used in this article series. Therefore we ask our readers, IF they know that their specific mineral wool product is not made by this company that they keep in mind and use other synonyms for this mineral-fiber-based insulation product.

Article Series Contents


Continue reading at MINERAL WOOL / STONE WOOL ASBESTOS CONTENT or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.




Or see BALSAM WOOL BATT INSULATION - a cellulose product, not a mineral fiber




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